The obvious pessimist/realist take would be that all of the Fang Gang was killed protecting the innocent from the wrath of Wolfram and Hart. That would fit quite well with the theme of fighting unstoppable evil regardless of whether or not the battle can be won. However, if one were to create a storyline in which Angel and the gang survive, I think that the gang would probably fight their way through the hordes of baddies and find the dimensional gate or whatever is releasing these minions into our dimension. The gang would jump through, kill the Senior Partners and all would live happily ever after. It is a little depressing that this is the most believable continuation that I could come up with that would involve the survival of the Fang Gang. 🙁