Problem is that the characters translate to crossover and merch. They all appeal to a niche demographic and if they kill any of them off they risk losing some player goodwill. They can try to reintroduce a new character in the same archetype, but that is always going to be a gamble, and more often than not is either poorly received or splits support (see Lyse).

If consumers as a whole didn't attach themselves so much to characters it might not be as much of a problem. But they do and like any franchise they can't really risk upsetting the balance.

They could kill Krile probably and be fine, but that wouldn't have any weight so why would they bother?