And of course, Spike spent a year hanging around on "Angel" after the train-wreck that was he and Buffy. Hell, Cordy made it until season four of Angel IIRC after her and Xander fell apart. Willow and Xander never even made it off the ground. There's the fact that Anya stuck around for a full year before they finally killed her off.
Hell there's probably even more I can't remember right now.