Good point. It’s not necessary for them to have died out, but merely only bred with females from the mitochondrial Eve line. Presumably this was one highly attractive lady! :)
How exactly do mitochondria pass from the father? There’s not enough room in a sperm cell to fit a mitochondrion. (Not that I don’t believe you; I’m just curious about the mechanism by which it happens.)
Everybody is curious. The existence of the phenomenon is frequently mentioned.