This is truly a dilemma. In your shoes, I would look at the big picture: has he done this sort of thing before? He could be having personal issues and turned to the bottle for solace.

I think you should give him a stern talking-to and perpharps a suspension or slight salary cut to further drive home your point, but I don't think you should fire him just yet.

Also, since you said you all are closely knitted, you could maybe try to find out if anything is wrong, or get someone else to if he'd be a little uncomfortable opening up to the boss lady.