you did the right thing.
interestingly enough i am going to face a very similar situation at work tomorrow. i already told people that i will be with, that i cannot drink "due to health issues"... they looked a little weired at me (possibly because i would be the first one celebrating in the past), but didn't really say anything one way or another. i still have to socialize, but i am not going to drink and if the pressure gets too much... get out, make up an excuse and get out.
if someone gets fired, or doesn't get promoted, for not taking a drink that's border line insane, imo.