Nicholas Brendon is in Rehab. *cries* Xander's my favourite character *coughusernamecough*
Dunno about the TV movies, the Giles one could be the Ripper spin-off. Alyson Hanningan's got Americana to do.
Spike, I don't think could hold a TV movie on his own. As Season Four of Buffy and Season Five of Angel showed. He's best being the annoying twit. That makes him so likable and funny. So he should be relegated to supporting character.
Andrew would be a good choice for another character. However, I doubt that SMG would be involved...hmm...Acker maybe for Illyria, since we only saw six (and two seconds) eps of her.
Tristy - Angel arrived to Sunnydale with an amulet from Wolfram and Hart for him to wear - but Buffy chose Spike and told Angel to make a second front, so that if the slayers lost, then Angel would take on the battle afterwards.
Buffy took the amulet to Spike (he had a soul as well) and it began to glow in the hellmouth when fighting the Turok-Hans. It then unleashed sunlight that destroyed all the uber-vamps and then destroyed him. It took the town with it.
HOWEVER, at the end of Conviction (Angel S5 opener), Angel got a letter with the amulet in it which had, not a ghost, but a spirtual form of Spike that was trapped in the amulet. It wasn't until Destiny when Lindsey made Spike corporeal, which sparked off a huge panic to who was the actual Shanshu Vampire.