In my comedies, nobody stays dead. It's fantasy, so there's plenty of reincarnation. To that end, unless it's central to the story (like one of the MCs dying at the end of book 3 to be reborn as such and such) I can kill off pretty much anybody I want whenever I want.
In book 2, one of the MCs became a ghost due to wayward magic, and it turned out to be a funny scene. He was brought back to life in the next chapter. I hadn't planned that at all - it was like good filler.
As for knowing their fates... well, I'm only on book 2, and I've planned 10 books, so yeah, I know a fair bit about their overall fates, but as far as what happens to them per book or per chapter, then no, I don't really know until I write it, or at least until I formally plan the outline of the book. One of my characters will never die, and she'll be important, but I don't know how yet. 2 of my characters will get married, but I don't know when yet (I do know who, but only after writing half of book 2, even though both MCs were in book 1 aswell).
In my NaNo, I've planned a supernatural murder mystery, and I've spent a couple hours per day for the last 2 days planning the book, so I have a pretty good idea of who gets it. Often, I know how they get it, too. There's 1 I'm undecided on, 1 I don't know how she gets it, and 1 I really don't know how to kill in the slightest just yet... like I said - supernatural. Actually, change that undecided one - he gets it.

Boy, I'm bloodthirsty this morning!
So yeah, I tend to plan things out, either on paper or in my head, so I know most of what is going to happen long before writing it, but there's still plenty of room to surprise myself. It's usually only the things which are majorly important to the storyline that I know beforehand.
Cliff