Rituals matter.
If the drinking is a ritual, well, I'd suggest they should find a better ritual, still...
I was co-leader of a band years ago. We had an absolute rule: no alcohol for band members during rehearsal or performances.
Then one night...
We were playing a song where there were two guitar solos. One guitarist played one, the other played the other. All night long this guy had been pushing shots of tequila on us, all night long we'd been refusing them, giving them to our fans instead.
There was a tray of shots on the edge of the stage.
The first solo was approaching.
Guitarist #1 was doing the usual set up thing he did a measure or two before this solo (not sure why this one was like that, he didn't usually "set up" for a solo like that). He saw the tray. Walked up, grabbed a shot and drank it the way you do a shot, head back, one swallow.
Then proceeded to rip out a brilliant solo.
Guitarist #2 followed suit.
As we were packing up I said to him, "This is where, as a band leader, I'm supposed to yell at you for breaking one of the cardinal rules of the band. But I can't. It was just such a rock-n-roll thing to do, I just can't bring myself to be angry about it."
This led to the ritual of the entire band starting the last set with a shot every gig. It was a stupid ritual. We could have played just fine without it. But we all had a little more fun because of that stupid ritual. I don't think the alcohol was even a factor, just the ritual.
You don't work music, you play it.
Discipline is not the enemy of fun.