Re: Sensei -- drinking??
You might not want to think about it that way, but sensei being intoxicated on the mat really could end up in an accident and someone getting hurt. I wouldn't tip toe around the issue too long.
Nowadays, if I got on the mat and smelled alcohol on the teacher's breath, I'd get off the mat again right away. I can imagine that that is hard to do as a more junior student.
It might feel like overreacting, since no one has gotten injured yet. Then again, if someone did get hurt, of course by that time it's too late to overreact. Really you'll be doing your teacher a big favor if you help prevent that situation from happening.