How do you want the death to impact your main character emotionally? I think that's the question, rather than how you want it to impact the reader. There really is no reason for the reader to become emotionally invested in a book's minor characters.
Your MC's mum dies in a fire. Okay. You could show a prologue about the boy and his mum and show how happy they were together, blah, blah, blah... and then show the fire and she die, and him go off on his quest.
But ask yourself this... would you as a reader, read a prologue? How many readers actually read the prologue? Not very many actually.
As a general rule, never put anything important that could be skipped in the prologue because most readers skip the prologue.
You have a story to tell and the story is the boy's quest which happens after his mum died, right?
Okay, so start the story right there, right at the point of his leaving for his quest. There is no reason to put in the back story of why he went on his quest, right at the beginning.
Or, you don't even have to start the story at the beginning of the quest, for that matter.
If you want to start out with the fire, a better place might be, to start with the fire, just as it's ending... tell a paragraph that reads something like this...
See, now, in this example, I did not write a big scene about the deaths or the fire, but rather, I wrote this as the opening scene of the novel, with the character, telling his friends what happened. But I did not include all the details of the death or the fire. I only included enough to tell the reader:
This sets the paces of the story, without bogging the reader down in unnecessary details. No reason to put the fire or the deaths on the page.
I always find it best practice, if you can move something to dialogue, to do so. Dialogue moves faster and doesn't leave the reader skipping over large blocks of narrative text.
If he was emotionally close to his mum, then the death could have a lasting impact throughout the story, with him constantly referencing back to "My mum used to do___" and "I miss my mum's cooking" etc. Show him grieving and the readers will feel sad with him.
This helps the reader to feel emotion for the character, by showing them he is sad. They don't need to know his mum. They only need to know that he misses his mum.
Of course, if you have plot reasons for showing the fire and her death then there is no reason to not show it. It's your story after all and you know what you want to tell your readers.
You may not even have to show the death or introduce the mum, but rather start the story with him doing his questing stuff, then at some point before the end of the first chapter show him telling another character: "They murdered my mum, you know." He doesn't even have to go into full detail yet. Just that one line tells the reader his mum is dead and someone killed her.
You could continue on in this way, with him dropping clues about her death in conversations, but never describing the full scene of her death in detail and letting the reader put the puzzle pieces together on their own.
In my long running series, Quaraun's mother died when he was 3 years old and he witnessed her murder. It traumatized him, but the incident is not even mentioned until the 3rd novel of the series. Throughout the series you see him mention his mum's death, but if you start to pay attention, you'll notice he describes it different every time, and those close to him, start to realize, he was so young when it happened, that he really doesn't know what happened.
Now, I have other characters in the series, who's mums died, but, it'll just be mentioned in passing and no details given, because for those characters, the deaths are not important to the plot. But for Quaraun, his mum's death is important, because it was the shock of witnessing her death that resulted in his warped view of certain people in his life. So in this case, knowing details of his mum's death becomes important, because it hints to certain aspects of other characters.
At no point however is the mother ever introduced as a character, nor is her death scene ever put on the page. This is because there is no need for the reader to get to know her as a character and, leaving the details of her death unknown, is a plot device, which allows the reader to see Quaraun as an unreliable narrator.
So, you see, how you write the death itself, is important to the way you want to reader to see the story.
In some stories, getting to know the dead character, may be important for the reader, and I've seen some authors do it where they rotate chapters. Say,
Etc. Like that, so that the reader gets to know the character's mum a little at a time.
It all depends on the type of story you want to tell and how you wish to convey it. So there's really no right or wrong answer here.
The character death on the way a few chapters in, could be a bit more difficult, if you are trying to go for tear jerking the readers. You'd have to really put the to-be-killed-character right front and center, almost to the point of feeling like he was the main character, so readers are really rooting for him and then BAM, he's dead and readers are... wait...what? But... but... wasn't that the main character? Then the real main character takes over. I've never written a story that used this sort of thing, so not sure exactly how one would go about it.
As for the everyone in the village dying... Quaraun is seen by people in his world as sort of a jinx because every time he arrives at a village, it ends up razed or something.
So, I've written several dead village scenes, and the way I do it, is to show him arrive and have a scene of him interacting with people, show the town/village/city as more a less a nice happy place to live, show a few families living their lives. Nothing big, just, so the reader goes "awh what a cute couple, what a nice family" that sort of thing. Then move on to Quaraun doing his thing, moving the story along, then BOOM, without warning cut to a scene where the city is in ruins, charred bodies in the street, smoldering houses, and Quaraun is standing watching this... He's all "Oh no, not again" and the reader knows the people he just meet are all dead, but the deaths are not on page. It lets the reader know everyone in the village is dead without doing a scene by scene death of each person.
Again it depends on the type of story you want to tell and how you wish to convey it. So there's really no right or wrong answer here.
As for, should a character exist just to die.... yeah, I do that a lot.
My latest novel in the series for example, Quaraun comes to this village where child sacrifices are happening and he rescues this little boy early in the novel. The boy's parents have already been murdered, and he can not find any relatives, so having lost his own children, takes the boy in as his own son.
You see a very close relationship form over the course of the novel, between Quaraun and Elwin and the story leads the reader to believe they'll be seeing the boy as a regular character throughout the rest of the series.... until the very final scene of the novel when the boy accidently falls into a trap and bleeds to death before Quaraun can get him out of it.
While the death serves no purpose in this particular novel.... the death is important to the next novel in the series, when Quaraun is now seen as emotionally crushed after the boy's death and it brings back PTSD flashbacks of the deaths of his own children.
The boy in this novel, existed for one purpose: to die and trigger a mental meltdown Quaraun would have in a future novel.
So, yes, characters can exist for the purpose of dying. They often do.
Of course, it also happens that a character starts to hold the story back and becomes a drudgery to write.
And let's face it, if a character starts to bore the author, you can be certain they are boring the reader as well.
This is a case of the character has served their purpose and using them any longer takes away from the story. So you now have the choice of sending the character away or killing them off.
This happened to BeaLuna and Bullgaar.
Originally two of the series' primary characters, I simply grew bored of writing them. I began to find it difficult to find useful places for them in the story, and so I wrote a story in which Quaraun actively tries to get rid of them.
In The Vampire Leprechaun of Fire Mountain, the final scene ends with a new character showing up and warning BeaLuna and Bullgaar to stop following the Necromancer. FarDarrig tells them that if they continue on this path, they will soon die.
They assume FarDarrig's warning to be a threat...
...until in the very next novel (The Obsidian Idol of the Elf Eater of Pepper Valley) Quaraun has had it with their bullying him and tries to sacrifice them on an altar. They escape at this point, and Quaraun travels on without them.
However they meet up again for a brief scene in The Vulgar Alchemist Inn, when BeaLuna and Bullgaar, turn on Quaraun's lover Unicorn, accusing Unicorn of being the cause of Quaraun's increasingly evil behaviour. Quaraun is torn between loyalty to his friends and loyalty to his lover, and ultimately tells them to leave and not come back, choosing to stay with his lover, Unicorn.
The duo sees their last use in volume 8 of the series, when BeaLuna and Bullgaar, worried about Quaraun's failing mental stability, once again join him in his travels, this time as they trek across the Valley of the Katopis in search of a healer for the dying Unicorn.
In Quaraun and The Vampire, Into The Swamp of Death, the following events unfold:
Resulting in two characters who were no longer serving any plot purpose, being removed from the series, via a very dramatic death scene that ushered them out on a new story arch that was created to further show the reader, main character Quaraun, is in fact not the hero but the villain of the series.
It took so many volumes to remove these characters from the series, because I kept thinking there might be a place for them later on. In the end, they were bogging the story down, so I instead of chasing them away yet again, I just had Quaraun kill them and be done with it.
So this is an example of taking a character death and using it to push the story forward. In this case, it shows the reader once and for all, that the rumors are true and Quaraun really is the evil villain, the people of his world claim his is. Up to that point in the series, the reader sees him only as a hero, and is never fully made to realize that in spite of being the main character he is also the main villain of the world he lives in.
Thus I took a character death and made it meaningful to the plot.
I could have simply had BeaLuna and Bullgaar die in a mudslide or something, far less dramatic then the ritualistic sacrifice Quaraun used to dismember them, but that would have had not real impact on the story, the plot, or the main character.
So, when killing off your minor characters, always look for a way that will move the story plot forward rather than just having them die for no real reason other then to remove them from the story.
In the end, my goal is never to draw the reader towards the characters who died, but rather to draw the reader closer to Quaraun. He is affected by the deaths, yes, but the readers are affected by his responses to the deaths. The readers do not care about Quaraun's dead mum, but they care about him, and feel sad with him, because he feels sad, not because they feel anything for the mum or the dead friend, or whatever.
In the end, it's your novel, you know the story you want to tell, so write it your way.
What do you want to become?
What did you do today to step closer to that goal?
Whatever you do, be your best at it!
And remember to have yourself a great and wonderfully glorious day!