I kinda know how you feel, you booked a flight and told your friends you would be there. Now you are worried about not following through on that and disapointing them. If it were just a trip with your friends you used to drink with, I would still be apprehensive. The way you described it as a drinkfest though should leave no doubt. The very, very best you could hope for is to be one very miserable chaperone. Why set yourself up for failure? Do what has to be done...