Yeah, that heart-stopping thing might be interesting in a "what if" kind of way, but no, what I'm talking about is something different. Seriously White Avenger? You haven't heard it before? I thought it was widely known. Oh well I'll air it out one more time. It's not a what if kind of supposition such as the one you and BotD are suggesting. This one suggests the slayer line quite possibly does run through Buffy now, and to believe that all you have to do is believe what the text tells you.
OK, I'll spell that out for you.
In Season 3 Marti Noxon said the line could only run through Faith. Buffy died, and the line jumped to Kendra. Kendra died. The line jumped to Faith. Later in Season 5 Buffy died again. Previous to Season 6 the press asked Joss if there could have been another slayer called as a result of Buffy's death in The Gift. Joss said no, because the line ran through Faith at that point. That much I'm sure of. I think he might have also said that couldn't change unless the writers could think of a way, but I can't find that quote.
Doesn't matter though, because at the end of Season 7 we learn the rule can change. The line passes without Faith dying. So it is possible. The question then becomes is there any evidence the line jumped between Joss's "only through Faith" comment, and the obvious contradiction to that rule. It turns out there is.
In Potential Buffy tells the potentials the line can now pass through her. Now that could just be something Buffy said to motivate the girls, but later Dawn is concerned, because she thinks she might be a potential, and the only way to be a slayer as far as she knows would be for Buffy to die. Xander, Anya, and Willow appear to share this belief. The argument to that is well maybe the Scoobs don't know any better. The problem with that is Cordelia described the way she thought the line had jumped through dead Buffy to Kendra in an episode of season 3. The Scoobs did not contradict her. Also, I forget which episode but Giles described the process in another earlier episode.
But none of that even matters because in Chosen we get the clincher. The episode is written by Joss Whedon, and the First Evil tells Buffy the potentials won't know slayer power unless Buffy dies.
Since that time even more support has appeared. In Season 8 No Future For You Roden refers to Buffy as "the last of the First".
Ok so if it's true, if the line now runs through Buffy how did that happen?
In Showtime Beljoxa's Eye tells us the First has appeared, because a disruption has recently been created in the slayer line. The First Evil plans to exploit that disruption. Beljoxa's Eye says the slayer caused it. In fact, that's important so let's quote.
GILES
If The First has been around for all time, then why hasn't it attempted something like this before? Why now?
BELJOXA'S EYE
The opportunity has only recently presented itself.
GILES
Opportunity?
BELJOXA'S EYE
The mystical forces surrounding the chosen line have become irrevocably altered, become unstable, vulnerable.
ANYA
Something The First did?
BELJOXA'S EYE
The First Evil did not cause the disruption, only seized upon it to extinguish the lives of the chosen forever.
GILES
Then what has caused the disruption? What—what is responsible for letting this happen?
BELJOXA'S EYE
The slayer.
But how did the slayer cause the disruption? And notice here Beljoxa's Eye is referring to
"The" Slayer.
Anyway they give us the answer. It's cryptic, but they give it to us.
ANYA
(limping) Yeah, I just—I don't understand how Buffy's death mucked up the whole slayer mojo. You know, it's not like she hasn't died before.
GILES
It's not because she died. The Beljoxa's Eye was quite clear about that in its enigmatic way. It's because she lives. Again. Buffy's not responsible for that.
ANYA
Oh. Oh. Willow and me and Xander and Tara. We're the ones who brought Buffy back. We're—we're the reason The First is here, the reason those girls were murdered. No, it's our fault. The world would've been better off if Buffy had just stayed dead. (walks off)
As we know there are consequences to heavy magic in the Buffyverse. The resurrection spell was among the heaviest. When Willow brought back Buffy it disrupted the slayer line in some way. How is the slayer line disrupted? In the episode following this one we start getting told the slayer line now passes through Buffy.
So there you have it the Buffy-Boards version of the "No longer through Faith" theory in the form it has evolved into over I forget how many years, about 30 or more tellings, and countless spirited debates.
BEG knows this theory well, and like me no doubt assumes everybody else knows it as well. So I guess what he's really asking is assuming the line now passes through Buffy, if Buffy dies in Fray's future, will she activate a potential there as slayer? Come to think of it if Buffy and Fray die could they activate 2.