My victory condition, like FT's, doesn't require me to eliminate anyone. I think a lack of deaths sounds like a state of Peace, which ultimately is what town wants to achieve against scum.
And since you find it "hard to believe" that I can win when there are no deaths at night, the more interesting question is why you can't win without killing at night.
In any vanilla game of Mafia, the aim is simple: the town is aiming to exterminate the Mafia. The Mafia is aiming to kill enough of the town so that they hold a majority vote. All Mafia games build off of this, in some way- vigilantes give the town a night kill. Doctors prevent a night kill. The cult gives an alternate win condition that simultaneously competes with the Mafia. The jester tries to get himself killed, and so on.
I'm not exactly sure why this is a mind-blowing concept for you, but I'll spell it out: I win when all threats to Ankh-Morpork have been eliminated.
I'm inferring that this means I'm against the Hippos, although the wording is vague enough that it could include others as well (for example, a serial killer or a cult).
I hope this also explains why I want to nail down the vampire question once and for all.