Buffy: The Vampire Slayer - Who"s the Next Slayer?
Throughout season 7 Buffy gives many speeches to the potential slayers stating that if she dies one of them will be called upon to be the next slayer. But when Buffy died at the end of season 5, there was no slayer called upon because Faith is the active slayer, not Buffy. Which means if Buffy died, no slayer would be called upon.
Season 7 of Buffy the Vampire Slayer