This is a real bummer.
33 years on skis, but I don't wear a helmet - even after the 20' fall that tore my shoulder up and knocked me out. If I die on skis, I'll have died happy. I've even told my parents this. Heck, I don't wear pads/helmet rollerblading and the one crash where I hit my head, the helmet wouldn't have helped anyway. OK, I'm being stubborn...
Every sport has its risks, even Yoga...
EDIT: Interesting article on head injuries and how little a hit, can cause death.
http://www.cnn.com/2009/HEALTH/03/18/brain.injury/index.html