Much depends on the specific conditions of your mishap.
If you're drunk and sink a boat with loss of life you'll be in a big heap-o-trouble and maybe liable for the full price of the boat, personal injury damages ($ millions) and perhaps even criminal charges.
If things simply get away from you and you ding a keel, you'll probably lose your deposit, and maybe even the balance of your trip if the damage is so bad you can't sail the boat. (Consider bringing a boat back with 2-feet of keel missing and asking if they will give you a new boat!).
Bottom line - If you sail like you would if the rule is "you break it, you bought it" you'll probably be fine.