Right until the final episode, various characters quote a prophecy that says, more or less, "Beware the witch with the blood of the lion and the wolf, for she will destroy the Children of the Night," which drives a lot of the fear surrounding Diana (whom most people seem to take for that witch), though Satu often claims that she is that witch.
I am unclear on whether the Children of the Night are vampires, as seems most likely, or all supernatural entities. Regardless, at the end of the show no one seems to have destroyed any of the supernatural groupings, and they seem on track to be stronger than ever, with the reason for their decline identified and addressed. They have only been in destroyed in the very metaphorical (and bigoted) sense that there are no longer legal barriers to intergroup couplings—that is to say, not in any sense at all, because the groups were always descended from daemons in the first place. This would be the destruction of vampires in rather the same way that the revelation of Neanderthal DNA in the human genome was the destruction of Homo sapiens.
Nor is it clear what the blood of the lion and the wolf is, or how Satu or Diana would have it. (Sure, the latter is descended from daemons, but the whole point is that so is everyone).
So in the end, who was the witch of the prophecy, assuming that it was even correct or fulfilled?