I've had friends get struck by hit and run drunk drivers, and just people not paying attention. One was recently struck by a truck and speed so hard, she came out of her shoes! She was lucky to have suffered only a broken leg and thumb.
The hard reality is that what we do can be quite dangerous, and all the best intentions and practices can only reduce the probability of injury or death. That crash I has a few years ago was an eye-opener. I fractured the bottom of my skull (one of the occipetal condyles), and a little research made it clear I was very, very lucky it was not a displaced fracture, or I would likely be dead or a complete quad. I don't even know how it happened. That's a hard thing to swallow, and especially every time I find myself descending at any speed.
There really is nothing to say except I am sorry for your friend, his friends, and his family. It's tragic.
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Proud parent of a happy inner child ...