I have picked my children up when tipsy.
I often have a long wee and then sober up, it's very annoying on a night out.
I recover very quickly when I eat something as well.
So, as said, it depends on whether it is regular, then it would be worth mentioning it to the teacher.
Once in a while, is fine. I have left celebrations/leaving do's/wakes, picked up my children and dropped them off at my Mums/friends, then gone back out again.
It's less of a problem than sitting that night as a LP getting drunk in the house, as I know many do.
If it was a problem, all of the holiday/chalet/camping type places would close, because practically every parent drinks, with children in tow.