I don't know if Faith had enough of a fan following back then, but I could see it running for a Season or 2, maybe even 3.
Lots of things would have changed, though. For instance, I don't think Cordelia could have been part of Faith's world, so she might have stayed in Sunnydale, with maybe Xander jumping ship insted. Wesley would have been interesting to see, if his 'Rogue Demon Hunter' days still happened, or if he would have developed as much as he did. I can see Gunn fitting into Faith's life, maybe even as a love interest. Fred would be out, but Illyria might work.
It's interesting to think about all the stuff that would have changed, or never happened but, as usual, this girl keeps circling back on one thing...if Angel stayed in hell, and never came back, then there would be no Connor!!!
Yep, I'm obsessed.