Okay, up-front, I just want to say that I'm
answering the question in the title, not actually asking it. I have a theory that I haven't seen anyone mention so I'm gonna put it out there because why not.
Alright, so. Here's what we know: The Oracle of the Sunken Valley prophesied that
"Belkar will draw his last breath- ever- before the end of the year."
Now, obviously, the interpretation of "Belkar dies and goes to Hell" is a completely reasonable one. I don't blame anyone for taking the prophecy at face value and assuming he's just gonna straight-up die, no frills. That's reasonable, and if it's what ends up happening, I won't have any trouble accepting that.
But here's the thing:
Vampires don't breathe. There's a vampire-shaped loose end running around, and it's entirely possible she's there for more than just giving Hel and Loki something to talk about briefly before they move into "I'll kill you!"
The Teal Deer(TL;DR) here is, "what if Belkar fulfills the Oracle's prophecy by becoming a vampire?"