Many thanks. :)
I'm looking for an au fic where Tara dies, and Willow goes very evil, and curses the Scoobies. She takes Rupert's knowledge, and he dies because he doesn't know about the bad things in the night. She somehow destroys Dawn, unmaking her. Buffy dies I think because Willow took her slayer strength. Xander becomes immortal, destined to watch everyone he loves die. With the added angst of being able to get a woman pregnant, so then he'd have to watch any children he had die as well. Which makes Xan decide to stick to men, since at least that way no kids to love and lose.
Xander winds up (after 20 or 30 years) back in Sunnydale. Spike is there, as William. William knows he's a vamp, but has no memory of Spike's unlife. Spike went to Africa, got his soul, came back, found everyone dead ... and retreated, letting William take over. Xander and William meet, get involved, and something happens that brings Spike to the fore. Spike drains Xander ... who of course comes back to life. And then at some point, somehow, Spike and William are split, and the three of them (Spike, William, and Xander) stay together until William's death.
Eventually, Spike and Xander find Willow (who became a vengeance demon) and make her pay.
I'm searching through all my bookmarks, but haven't found it yet. Can anyone remember this one? Thanks bunches.