The best musical partner I ever had, with whom I did a duet for over 10 years, was a lush. When we finally broke up, it was because of the booze, and I'll be the first to say that I let it go on way too long, trying to cope and trying to get him to stop drowning whatever it was he drowns. I should have quit playing with him the first time he got too drunk to keep up with the songs, help break down and load the equipment, or drive home. Or at least put my foot down about his ever drinking on the job again.
I myself am not married to strict sobriety at a gig, especially when playing for a room of drinking folks, but I have an hard and fast rule that I take no more than one drink an hour if I'm performing, and I'm going to nurse each one. I usually tell the bartender I want water or ginger ale and, if available, a slice of lemon to clear the throat. And if anyone wants to show they appreciate us, they can put money in the tip jar.
And I won't stay and be polite about performers who get soused or stoned and expect me to join in their "fun." I'm outta there, and asking for my money back on the way out the door. I don't think it's doing them any kind of favor to be polite about having spent my dollars to see a sloppy show.