Shellcrusher- I was afraid to set limits for a long time - even those to keep my children safer (the same as you-- drinking while he was alone with them) because I was afraid of the threats AH made about how he'd involve the courts (and he did call the police when I took the girls and left last Spring and acted like I'd kidnapped them) and I'd wind up with no custody at all. I let my fear (and they were legit fears, like yours) stop me from doing what I had to.
What's happened in the past year as I have stood up to AH more and more in ways that keep the girls safer is that his threats have proven to be hollow promises. He's lots of talk and no action and while I don't know your wife one bit, I'd be really wary of not fighting to send him to day care just bc your wife threatens to involve her lawyer and fight you on it. I'd be willing to bet that's an idle threat. After all, how is she legitimately going to explain that she has been passed out drunk with a 2 yr old and with that info still have a leg to stand on for saying your 2 yr old ought not be in day care.
I'd make hard and fast plans to keep him in daycare and tell your W that's the plan and why (though I am guessing she knows full well why and her pride is what's wounded here-- not her belief that she will really be okay to be with your son 24:7 this summer).
Don't chance it is my advice. And don't let threats stop you from doing what you can to keep your son safe. Someone told me this early this Fall and I had a hard time believing it but it turns out that looking the threats squarely in the eye and saying (with my actions) 'threaten all you want, I am putting the girls first' has resulted in zero action from AH to keep any of his threats.