If someone HAS to die this season, almost certainly it won't be Buffy, Spike, Faith, or Angel, since they are the two series' main characters (notice, i said ALMOST certainly. We can't rule anything out with Joss) especially since all four have already done the "die and come back" thing once, if you count Faith's coma. And we know that Dark Willow is still alive during Fray's time. That leaves Xander, Dawn, and Andrew who have never died so far. Assuming that Season 9 has to end with a funeral, I would put my money on one or more of them.
Then again, maybe Joss will (seemingly) kill everybody, and Season 10 will open with all of the characters scattered about in another dimension, and the only way to escape is to somehow find each other and fight their way out.