kspuffykHi there,
I was looking a long time for a story very similar to this one and I've found it today. Not sure if it's the one you were thining about but Buffy was shown the future in this one. After Buffy was killed by the Master she looses the slayer or is offered it to become a Guardian. The story was about Buffy becoming a guardian, the updates ended when she met Spike (it's a WIP):
What If I'm Not the Slayer? by Caro Mio / LJ caromiofic
Canon to the end of Season 1. Instead of re-awakening as a Slayer, Buffy's powers have passed on. How will she adjust to being a normal girl, and is it permanent? Is this the one you're looking for?