Well... Our opinion is simple. We advise you to be insured in case of an accident (rescue service is expensive in France!).
However... before your ski vacation have a look at your daily insurance, they may covered you for those kind of accident. There is no use to pay an insurance if you already have one...
- If you pay with your credit card your skipass, you can sometimes be covered in case of an accident, call your bank to check.
- Your civil insurance can sometimes cover some ski accident (but it's not common). Call it to check and be sure.