I think if season 7 wasn't going to be the last one, it would have been very different. I don't think they would have destroyed Sunnydale or awakened all the potentials in the finale for starters.
But imagining that at the last minute, everyone decided a season 8 was going to happen right after Chosen was done... I can imagine it starting with a few episodes focusing on different people in different places. Like one with Buffy and Dawn, one with Xander, then Willow and Kennedy, Faith and Wood etc. Then after two - four episodes like that, have them reunite for a new (or old, they tend to be old) evil. Not sure where I'd have them all meet, maybe meet Giles in London, it works well for Angel and Faith.
I mentioned in another thread that a long time a go I had a season 8 planned where the awakening spell caused the demon essence that originally imbued the slayers to get pissy... or something like that. Can't remember much more than that though.