Voice-over is definitely the way to go. I remember Buffy doing the one at the end of the season 5 finale. It was very emotional. Perfect. My original thought was that Buffy should get the last line. Then I thought since she already did such a scene, maybe someone else should do it. So I voted Giles, especially since he is her watcher. I picture scenes being played of Buffy's life, with family, friends (scoobies), slayage, and etc. of her past, present and, at this point, questionable future. Giles would be talking over these scenes. His accent is a bonus too.