“Kill your darlings” is a common piece of advice given to writers. What it means, I suppose, is that when a character has run their course, it’s time to let them go. It isn’t an easy maxim to follow, but sometimes it has to be done.
That said, in speculative fiction, it’s easy enough to bring a character “back from the dead”, but only if doing so enhances the story and not because the writer can’t bear to be parted from one of their creations.
In my latest WIP, Through the Gloaming, I’ve had to make the decision to let some of the characters go, for two reasons. First, as mentioned above, they’ve run their course. Second, I want to introduce new characters and don’t want to confuse readers with too many names and faces. So they’re gone and while I’m sad to see their departure, there’s always the chance that at least one of them will make a reappearance in the third book of The Silver flute trilogy.
So, so long and farewell, my dear friends, but life and plot move on.