For myself, my monies on hypothermia.
don't know why, but I always imagine being stabbed down a side street somewhere
my money is on a lack of oxygen to the brain...
There was an article local freebe mag with some bloke about to go on a trip and try an climb mount Everest. He was posing for a picture with with one of these papoose kiddies things - i.e. his little kiddy strapped to his front.
Statistically if you attempt the last stretch of climbing Everest you have a 1/10 ~ 1/15 chance of dyeing, nothing to do with fitness, or training, or equipment - essentially some (to date unexplained phenomena to do with hypoxia).