Well, I would love for there to be a spin-off, on any of the characters, and some of the characters going to Angel would be good.
But if they don't do any of that, I'd want either of these two things to happen, either they defeat the first evil and they never have to battle evil again, or the entire cast dies. I know that's a little drastic, but I don't want to think they could be still having adventures after the show is over, and that's the only way I can think to do so.