Riding a bike slowly and cautiously and wearing a helmet. A near -0- chance of dying from a fall. He was not wearing a helment, going really fast, or his landing spot was not on a flat spot.
I saw a kid on a moped going maybe 15 mph fall and hit his head on the curb. Cracked his skull like a walnut. I never found out what happened to him. But even stationary small falls and crack the head badly. Especially for a guy in his late 70s.