It all depends on what the universe wants from them, needs from them, whatever magic voodoo nonsense went down.
In mythology, a vampire is a grotesque, evil demonic creature, but on earth, a vampire’s spirit basically takes the human body so they can use God’s wonderful creation, humans, against itself. It’s just another way for them to stir the pot and whatever. Vampires…smh.
I think the human soul dies, stays dead, but the vessel, the body stays fresh so long as a spirit or presence keeps it alive. With magic, different things can happen, like when Buffy died and came back, she was a skeleton and then got her flesh back because of the spell, her soul came back.
I think the biting thing is basically a summoning ritual that just calls the demon into the body. So keeping that in mind, other demons and their own spells/magic can probably have similar effects to what Willow did with Buffy. They became ash, and from ash, the body would reform from where the demon spirit originally was, in the dead body of human. So the body dissolves, but the demonic presence returns to hell. And backwards, the demonic presence returns to earth, and it’s original vessel reforms so it has someplace to live.
I’m still figuring out the soul part, though.
BTW! This is all my theory . This is the stuff I think about in the shower, XDXDXD