Right now you're living in "what if" land because of a choice you think that he might possibly be making tonight. Nothing has actually happened yet.
What it you take this one moment at a time. Get out to your meeting or spend some quality time with the kids (great suggestion by Earthworm) or whatever you feel will make you the happiest tonight. Then take some quiet time, away from the chaos of his choices to think about what YOU want YOUR boundaries to be. This really isn't about his decision to drink, but about what you are willing to accept in your life and your home and your marriage.
Big hugs to you and your kids.