As long as they apply it fairly, I don't see an issue - normal holiday drinking, slightly more than normal but not totally pissed and unconcious, and you have an accident - they should pay out.
I wouldn't agree with a 'we won't pay if you have had a drink at all/are over the drink drive limit but not parylitic' policy, because most people think it is reasonable to drink a bit more than usual/is healthy when on holiday.
I probably drink a bottle of wine a day while on holiday, but am never drunk as it is over a few hours but I wouldn't drink anywhere near that amount at home.
But for people who end up hospital needing to have stomach pumped, balcony jumping sort of level - maybe they shouldn't pay out. But then we risk people having to sell houses to pay the medical bills of them/young adult DCs who've had accidents while very pissed abroad.