Hi snood,
I hope you do attend your dinner, even if you're going stag. By not going YOU are depriving yourself of something YOU want but you're using your wife as an excuse to deprive yourself. Go, enjoy yourself! Have fun!
As far as your wife goes, why do you pay attention to how much she drinks? She's an adult and if she's paying for her own alcohol then she has every right to drink it. Because her friend thinks she shouldn't go grocery shopping after drinking at lunch does not vindicate your feelings that your wife is an alcoholic. Are you hoping your wife will change? Why would she change?