I have a feeling your real question is something else, because this isn't difficult to figure out if you're fully prepared to go hard core.
The easiest thing is call the non-emergency # of your cops, explain the situation, and ask if it's legal in your city for someone to be drunk behind the wheel of a car, even if it's turned off and the person is sound asleep. In many places, this is not legal. If yours is one of them, just call the cops as soon as he shows up.
A restraining order produces the same result, but it takes a little time and effort to get it in place. The cops can tell you what to do to get one.
I'm just guessing here, but if you're still married to his mom, and she's not on the same page with you, get her to an Alanon meeting. She needs to understand she's literally killing him with "kindness".