Ive never heard of anybody ever dieing from it, although I could see it happening in freak cases. If I had a pace maker I might be a little more careful but the only real risk I consider from it is a lot of pain and a tiny arc burn where there was electrical contact. If you are dumb enough to purposefully stick your finger in a spark plug hole and crank the engine though I think that is on you. You shouldn't have your hands in the engine compartment at all when cranking a motor unless you are an expert already.