In this particular context, I'd say the worst possible fate would have to be either of the following:
Generally speaking, a Yandere's obsession comes from a place of earnestness, their affections are genuine and nothing is more important than a darling feeling loved and happy. Yangire on the other hand don't actually care about how their object of obsession feels, and may even like seeing them suffer. The Yangire wants a turbulent, violent, abusive relationship because they get off on that shit. Despite the popular perception of the trope, I'd actually think the Yangire is more likely to do things like tie their obsession to a chair or chain them up than a Yandere every actually would, because at least a Yandere would be considerate about their darling's feelings.
Hell, I'd argue the two are, or should be, natural enemies.