I would express my feelings and then let him decide whether he thinks he is strong enough to resist temptation.
I agree with you that I don't see why he would even consider going since I'm assuming that anyone that goes out of the country for a week long bachelor party is expecting to go all out and drink all day every day.
If he is still taking everything you say extremely personally and it ends with him feeling bad about himself, it sounds like he isn't fully there in his recovery yet. Sure he might be sober, but as a recovered addict I can tell you, being sober is only part of the fight.