Killing off a character is a super-significant major event that both the in-universe characters and out-of-universe writer shouldn't avert one's eyes from it. Not only you are going to lose a character forever so plot may progress differently, but the acknowledgement of death will alter the mental condition and thinking pattern of some characters, so they may not think in the same way as before. Thus it is an important plot turning point where many things will start to progress in a different manner than previously.
Even the killed off character is just some nameless passer-by that has absolute no relationship with any of the main characters, it is still impossible for ones to refuse to acknowledge this thing called death exist in the universe, and although to a much lesser degree of death of a closer relative, still the acknowledgement of death will still affect the mental of other characters.
Also, with the existence of death, despite that one may not really utilize it at all into the plot of the fic, but the possibility of death will still set the tone to a more serious one where that greatly eliminates the overall comicality of the fic.
In the second fic I'm currently working on, I had already set up quite some deaths of a few pokemons and one human character, all as part of the background story told by flashback of one of my main character. It is important as it gives out the reason of why this character is behaving like he is currently, what difficulty he is currently facing, and what he can do to resolve his problem. And, by doing that as early as on Chp.2, the reader should then understand from a very early stage that this fic of mine is not anything comical at all, the story is serious, this PokeWorld is the raw world of survival where law of jungle is the rule.
Thought, yet, other than this death in the flashback, there is really no more death in any of the later chapters (or correctly speaking, not planned yet. But I don't think it is needed).
But on the other hand, I planned on severely injuring one of the main character so he will be put on bus forever. Not exactly death, but still, the mental impact to my main characters are really not worse than death itself happening at that spot.