Same thing kind of happened to a mate of mine. Lifelong skier, really skilled. Skiing in Austria with his adult daughter, he was descending at speed off-piste, a ski hit a rock and pitched him downslope into a tree. He was wearing a helmet, but clobbering a tree with your head at 30mph is not going to end well. Helicoptered off the hill, he ended up in the neurology ward for quite a long time.
He's kind of recovered five or six years on, but still has some problems in concentrating. Which is tough for a serial entrepreneur. He was CEO of his latest company before the accident.
Nothing like as bad as Michael Schumacher's skiing accident which reduced him to being a pale shadow of his former self, wheelchair bound and with difficulty in communicating. He apparently manages to watch F1 on the television and understand what he's seeing.
Or Fabio Casertelli in the 1995 Tour de France, who lost control while descending the col de Portet d'Aspet at speed (usually 50mph plus), and his head hit a concrete bollard at the side of the road. Dead at the scene. Not wearing a helmet, which was not necessary on mountain stages at that time.