People seem to feel strongly about the epilogue at the end of The Endless Forest: they love it, or they really, really do not love it.
I wrote it because I personally needed to have some closure, and to say goodbye to my characters. The idea that they were wandering around out there in the world and having adventures without me just did not sit well.
There are people who like surprises, and people who don’t. I do not like surprises. I prefer to know. And thus the epilogue.
As to how I decided about each character: I often flipped a coin. Is person x going to die in his sleep in a happy old age, or die in his forties, unhappily? Sometimes I just know — I know what happened to Simon, for example, but other times I need a push. This is one of those odd things about writing that is hard to explain.