That includes a number of assumptions.

First: do vampires have nefesh? If they don't, then would pikuach nefesh apply?

Vampires, according to some mythologies, don't breathe, which means that they don't have ruach. And since nefesh is a higher form of soul than ruach, and builds upon that soul, then you could argue that they can't have nefesh. And therefore, they aren't subject to the rules on pikuach nefesh.

If a vampire is dead, then how can it use the rules on preserving life?