As far as I had ever read about Empedocles, he threw himself into the volcano, not as a sacrifice, but to prove his immortality. The, probably, apocryphal story is that he walked into the volcano so that people would think he vanished and ascended into immortality, only to have the volcano spit his sandal back out to prove his deceit.
I’m unfamiliar with any story of his death as a sacrifice. I’d love to be enlightened.