I worked a season in a ski chalet as a gap year, and we had a few guest accidents. One lady went over on her shoulder first day, I helped her organise with her insurance company. They paid out, she got treatment and spent a week walking around the town or sat in the chalet reading and eating cheese. There was another woman who broke her leg AT THE AIRPORT. She fell over someone's suitcase and hadn't even made it to the resort. Insurance paid out, she had a cast on, her husband skiied all week and she stayed in bed on skype to her friends while I made her cups of mint tea. There was another couple where the lady broke her foot a week before the trip, but they'd done they're insurance so well it paid out and she still came and she had one of those knee scooter things. Then there was the 19 year old who broke her collarbone dancing on a table in the bar. Even she had insurance.
You know who DIDN'T have insurance? The upper middle class estate agent/landlord chap, who clearly thought he was so good he didn't need to get insurance. Two days in he tried to copy his friend going over a small bump. He got too much speed, knocked his friend over and into the queue of people waiting for the ski lift. While highly comical, he did his knee in and complained the rest of the week at how much is was costing him and how horrible the medical system is trying to screw him.
NEVER TAKE THAT GAMBLE
You have to buy insurance that starts the day you BOOK the holiday, in case something happens and you can't go. Then make sure it covers accidents and medical treatment. It's not even expensive! I pay like, £7 a year or something to have it as a bonus on my home insurance, and it covers extreme sports.