Not comic reader, so I always assumed that once the final freshly activated slayer dies there would be no more. Of course, the real pisser is all they needed was the amulet.
Possibly not. Without the extra Slayers to keep the ubervamps occupied, Spike, or whoever wore the amulet (in that scenario, I would have opted for Angel for the honor) might have been overwhelmed before its power kicked in.
I think the best fic ideas (what ifs) would come from the 900 who didn't join the army - focusing on the ones who decided this extra strength and healing ability gave them good opportunities to get rich and powerful. If some of them cooperated they could probably slowly take over the world.
Maybe I just imagined it, but wasn't something said at the beginning of Season 8 about those girls no longer being Slayers, like Willow somehow figured a way to selectively "turn off" their power? Maybe not, but I got that impression from somewhere.
Also, in the Frayverse- if that's still canon- no new slayers were called for a long time after Buffy's final battle. I just got the impression that when they run out of slayers that's it, no new ones.
I think that new girls continue to become Potentials, but, unless there is a need for one, like during the time between the last great battle in the early 21st Century, when that unnamed Slayer and all her friends somehow blew all of the vampires and demons in the world into a hell dimension, taking themselves along in the process, no Slayers were ever called, simply because there wasn't any need for one.
Also, in the "Fray" mini series, she is, apparently, the only Slayer Called, so it would appear that, once the last of the girls left from Willow's activation spell was gone, the system of "one girl in all the world" rebooted, but needed the return of the lurks (vampires) in Fray's time to restart the actual process of Calling a new Slayer.
See, this is one of the reasons I always thought it was irresponsible of Buffy & Willow to make all the potentials slayers.
Most likely, Buffy never had any idea just how far reaching the results of her plan would be. Remember, Giles told her that there were "only a handful" of Potentials left, and that they were all "heading for Sunnydale." The term "handful" doesn't bring to mind several thousand girls scattered all over the world, even if that is only a minuscule amount when compared to the world's population.It's quite possible that Giles and the Watchers in general had no idea just how many Potentials there actually were in the world. We don't have any idea just how, when, or why the individual Potentials were made, or how the Slayer is selected from that group, but possibly the Potentials identified and located by the Council were only those girls with the highest probability of actually becoming the Slayer. We know that at least a few go unnoticed prior to being Called, because Buffy was one of those. Merrick, her original Watcher, only approached her after she had been called, and Dana, the nut case from Season 5 "Angel" obviously had never had a Watcher, even before the First Evil set its plan into motion. Also, look at all of the girls who Willow's spell affected in "Chosen." Not a single one of them appeared to be, as Giles had said, "heading for Sunnydale," they were all going about their daily lives, completely oblivious to what they had been before being activated.