Vampiric afterlife? Not sure, except that Buffy's generally happy to help them get to wherever that is.
Seriously, I'd like to imagine it can vary. In Oblivion, five of Azura's followers killed the ancient vampire Dratik and his kin holed up in Gutted Mine. In the process though, all five were infected. Azura sealed them up in the mine until her Slayer came along to give them the freedom of death. Buffy would like to think that somehow their spirits reside eternally with Azura, just as the five candles Azura placed above her shrine in their honor burn eternally.