What is the probability? Normally a fatality requires several conditions occurring at the same time like your buddy is not present or they did not see you or surface is far away, so, you have to multiply all probabilities that makes even smaller probability . A healthy human on land takes way more risks on their daily life than that risk. Otherwise we could not function.Uncommon but fatal if you don’t mitigate the problem. A large part of diver training is for events that are uncommon but in a reasonable population happen often enough to lead to an unacceptable death rate.