I think you made the right choice in not going. The guy lives there so your going essentially endorses their relationship when that isn't how you feel. It's not like you need to kick her out of your life. Invite her over to your place (by herself) for some fun family time next weekend.
I'm not in the once an abuser always an abuser camp (especially if he only has problems when drunk) but alcoholism is a tough disease to kick. If one wife already divorced him over it I'd be pretty surprised if he makes a major life change over being kicked out of the house for a short period.