Seems SMG was shooting Scooby Doo-Doo the day of the party. Though, before she left town, she gave the crew leather bound Thomas Guides of LA. I'm not familiar with them, but they seem to be a must have for actors and crew in Hollywood for finding location shoots.
The party itself may have not been so much an official wrap party for BtVS as for FOX. FOX neglected to invite the majority of the crew and most of those that were invited were told to leave their spouses at home. Plus, their was a higher number of photographers than are usually at these things.
I don't begrudge FOX for trying to get some publicity for the show, this just didn't seem like a fun time for those directly involved with it nor a proper thanks for all their hard work. It wasn't really for them so much as the press. Seems that the actors got out of there as soon as they could.
I can only hope for their sakes they got a decent, private party to say all their goodbyes (or, see you in the fall depending on any possible spin-offs). And, who knows, maybe SMG, ED, and others who weren't at this party were there instead.