What Would a helmet do in that situation? answer:nothing. He would get as messed up with a helmet on. but it is crazy. and yes he should have landed that cliff switch
depends how many rocks he hit with his head, I would rather hit 10 rocks with a helmet and have the helmet function for 3 of them than have no helmet at all and have my skull ripped apart and smashed... if he didnt die I'd attribute some of it to helmet...