I love that interpretation, since it plays on the cynicism and disrespect for monsters to cause Xykon's eventual downfall. (Though/And it raises some uncomfortable parallels with Lien's disappointing answer to Serini now.)
Well, yes. I have no doubt that he thought he killed her. I just think it's very careless in the OoTS world to assume someone's dead (and more importantly, unable to come back) just because they're a charred lump of raw meat.