OOC: Xander's AU
OCD-ridden and completely tl;dr.
What's changed in FH!Xander's Buffyverse from the canon version. You don't need to know this to play with him; if you play a Jossverse character and they assume he knows something he doesn't, that's A-OK. They would assume that; go with it. This is just for Big Jossverse Geeks who like to know this stuff purely because they like to know this stuff.
Basic split: at or around Graduation Day, they didn't blow up the school. They evacuated the students off to other cities, and in a couple cases, dimensions. Xander ended up at FH, Willow ended up at Hogwarts. (This happened when great reptiles roamed the earth and specific rules about canon-mixing hadn't been pinned down yet.)
People who are still alive in Xander's AU who died in canon:
Larry Blaisdell: (died in Graduation Day, which didn't happen in FH!Xander's timeline) Currently being the man-on-the-spot at the Cleveland hellmouth for Watchers' Council v. 2.0.
Harmony Kendall: (vamped in Graduation Day, which didn't happen in FH!Xander's timeline) Currently... someplace not Sunnydale.
Cordelia Chase: (in FH!Xander's timeline she ended up in NYC due to the school evacuation, stayed there for college, and never went to work for Angel) Currently... doing something on the east coast. Probably stage-acting.
Anya: (Xander still went to Prom with her. She was shipped off to another school, like everyone else. If she did come back in S4 to try to hook up with Xander again, he wasn't around to see her, being at FH.) Currently... good question.
Spike: (Well, vampire. Alive-ish. He was never souled1, thus didn't burn up in Chosen because he wasn't eligible to wear the tacky-amulet-of-doom. Currently wherever Buffy happens to be. Spike is unsouled and unchipped2, but [insert redemptionista stuff that I have no firm opinion on but it works for the story so *waves hands*] helping Buffy because he's in love with her (and by now has extended that to the people and things she cares about).
Jonathan Levinson: (After learning that a future version of himself was on the side of good, Andrew didn't abandon Warren and Team Evil Overlord, but it was enough of a nudge to make what happened in Dead Things be one step too far. Andrew was thus slightly less susceptible to the First Evil's impersonation of Warren, and didn't kill Jonathan.) Currently doing the east coast Slayer run for Watchers' Council v. 2.0.
Chloe: (The Potential Slayer who killed herself in season 7 due to the First Evil's influence. Here, Dawn was paying attention and noticed her missing from the group, so they saved her. ) Currently working with the Watchers' Council.
Most of the people who died on Angel: the series as some direct or indirect result of Connor's existence, since there's no such kiddo in Xander's universe: (Xander knew about the possibility of Angel fathering a child via FH!Callisto's unhappy experience, and he passed that on to his dimension's Angel, so no accidental bebiz with Darla.)
- Wesley Wyndam-Pryce: currently still at the Hyperion with Angel and Gunn, since no Connor = no taking over Wolfram and Hart
Fred Burkle: ...yeah, I have no idea. Not still in Pylea, because I'm not that cruel, but she might be with the Fang Gang or she might have gone home.
Lilah Morgan: Not dead, still working for Wolfram and Hart, was dating Wes we don't ask how, we just accept that no world needs to be without that pretty but the whole Tacky Amulet of Doom thing put a stop to that.
Everybody who died in Once More With Feeling: (Having lived through it at FH, there's no way this Xander would pull that stunt, plus the canon situation that motivated it doesn't exist.)
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People who died in Xander's AU who didn't die in canon:
Faith: (Wore the tacky-amulet-of-doom instead of Spike, and died in Chosen.)
[Season 8 Comics Spoiler...]: Warren Mears: In the tv series, he appears to die, to the point where a creature that can only impersonate dead people impersonates Warren. In the comics, it's revealed that Amy Madison was watching when Willow 'killed' him, and actually saved his life in a retcon that's still breaking my brain because see above re: First. Evil. Impersonated. Him. In FH!Xander's world, he's still dead as a doornail, because Amy had already left town at the end of Season 5, right after Buffy died. That change wasn't even to make sure Warren stayed dead, as I made it before the comics revealed that fact; it was actually so Amy wouldn't be, you know, buried under Sunnydale.
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People who died but not quite as they did in canon:
Joyce Summers: (due to, again, FH-related foreknowledge, she didn't die of an aneurysm, but that left her alive and in her own room a year later, where she was killed by the stray gunshot that killed Tara in canon.)
Tara Maclay: (She was still shot by Warren, but she was outside with the other Scoobies when it happened; she got the bullet that was meant for Buffy.)
Allen Francis Doyle: (Is.... probably still dead, but he didn't pass his visions on to Cordelia, because she wasn't there. Nor did he pass them on to Angel a la Cordelia's Birthday-verse AU, which we don't know for sure was a real alternate future anyway, since it came via a character who later turned out to be untrustworthy. Quite likely he just didn't pass them on at all.)
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Other people
Giles, Buffy, Dawn, Andrew, Willow, Kennedy, Robin Wood: still heading up or working for the rebuilt Watchers' Council. Dawn's also in college.
Angel and Gunn: still at the Hyperion with Wes, since no Connor = no taking over Wolfram and Hart
Oz: Wandering around the world someplace.
Amy Madison: Was de-ratted shortly before Willow got home from Hogwarts. Hung with the Scooby Gang for most of AU Season 5, but was freaked out/pissed-off by Willow using her as a battery to try to save Buffy during her fall from the Glory-tower. Got out of Sunnydale shortly after that and is...someplace. [Season 8 Comics spoiler...]Was not in Sunnydale during Season 6, and thus was not around when Warren Mears got DarthRosenberged; he's as dead as he seemed to be onscreen.
Riley Finn: It's entirely possible Buffy met Riley, but since she wasn't in college during S4, she only knew him as Yet Another Annoying Commando Guy. Which is kind of sad for Riley because canonically he grew a lot through his relationship with Buffy, but... chalk it up to not every change brought about by the AU is a positive one? (For complete purists who must. know. OMG: Giles, Buffy and Spike chased out the Initiative in a handwavy offscreen manner before it came down to the wire of needing to use the combo-Slayer spell against Adam.)
Lorne: Still owns Caritas v. 1.0, since the second time it was demolished in canon was all about Connor.
AU!Isabel and Parker: (Which will only mean anything to you if you've read Xander's adventures while he was away from Fandom.) Off doing their things as you might imagine they would be post their own canons. Xander might occasionally get mostly-handwavy e-mail from AU!Isabel, and he's going to poke FH!Parker with things about her that he shouldn't know but discovered via her older version, but I'm not planning on using them as a deus ex machina.
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Q: Are you taking the new season 8 comics into account?
A: ....maybe. If I feel like it. That's the nice thing about having taken it AU yet ending up in a similar place. Anything that makes me roll my eyes, there's probably a legitimate reason to say it never happened for FH!Xander. If it works, I might incorporate it.
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Footnotes. Which you knew there'd be.
1 When everyone went off to other schools, Buffy did too, at first, but then was sent back to Sunnydale once the Watchers' Council realized the Mayor-snake was still a problem. She stayed there with Giles for most of AU-Season-4 while Xander was at FH and Willow was off at Hogwarts. No graduation = no UC Sunnydale = no relationship with Riley + no Scoobies around + chipped vampire in Giles' bathtub = Buffy and Spike dealing with their UST by starting a relationship that didn't end up in the depression, distrust, and mutual-destructiveness of canon Season 6. Thus no souling.
2 Spike was present for Willow's dark magic rampage, and she de-chipped him at one point. Yes, this was entirely so I didn't have to deal with it disintegrating in season 7 since see above re: no Riley to come to the rescue.
3 Someday when my brain isn't leaking out my ears, there'll be links. Some of it's extrapolation, but most of the AU changes either occurred 'onscreen' for Xander or are at least referenced in discussion or an e-mail.