Okay, in the group shot, the two people most obvious by their absence are Dawn and Spike, and in the other, Buffy is holding a badly damaged Scythe. How's this: Dawn is used as the focal point of all of the magic in the universe, destroying the Twilight universe, shoving the bad things back into their own playgrounds, and sealing the dimensional walls so that nothing similar can ever happen again. In order to allow time for Willow to make the spell work, Spike, the Slayer's Champion (eat your hearts out, Bangels, Angel just ain't got the juice for the job) has to buy time by pulling a "300 Spartans," probably with a few Slayer volunteers to help, against the assorted opposition. The spell is successful, but Key and Champion are both lost when the Scythe, like an overloaded surge suppressor, burns out. Or, even more likely, Angel somehow sabotages the whole thing, leaving Spike and Dawn on the wrong side of the closed dimensional portal, making him the Betrayer we've been warned about.
Being the one to betray the whole group, for the "greater good," of course, in order to save the universe that he, through his own actions, was at least partially responsible for putting in jeopardy in the first place, is exactly the sort of thing that Angel/Twilight would do. Plus, if in doing so, he manages to become a real live boy again, (no magic in the universe means no vampires, demons, evil witches OR Slayers) all well and good. Human Buffy and white picket fence tossed in as a bonus. It's got Season 8 Angel motivation written all over it, and would be a perfect example of what he would consider making restitution for all of the bad that Twilight is responsible for.
Season 9 could then focus on Spike and the others who are trapped on the other side trying to survive and get back home.`
