Twice Bitten (Hermione Granger/Severus Snape)

Vampire!Snape. Yet another DH alternate ending. (Epilogue? What Epilogue?) Something dormant inside the dying Potions master awakens and turns him into a creature of the night. Is it possible to regain mortality, particularly without killing his minions Harry and Ron? Hermione helps out, of course. Humor, Adventure...