It sounds like the husband has social anxiety. He may drink too much as a cover. I had a boyfriend like this year's ago. He was a great guy but could be socially awkward in situations where he didn't know people. He was horrible at small talk and embarrassed me a few times. At least he knew he had an issue and would bow out of things that made him uncomfortable.  I'm surprised this couple didn't discuss this issue a while back considering they've been together long enough to have grown kids.  She should just come out and ask him if he wants to go (he may not want to) and if not she could go for a short time by herself and agree to meet him after for a movie or late dinner.