Eloping?

So my fiancé and I have not set a date or started planning because of his mom's severe alcoholism. She's blackout drunk, unable to stand up 99% of the time and she has so severely alienated his side of the family from her that she and his dad would be the only ones there. She won't even be able to show up because she can't physically go out in public. I've talked to my parents and they've suggested possibly eloping and maybe having a big wedding later, more than likely when my finances mother has actually drank herself to death. I know it hurts him so much to even think about his moms death and/or her not being at our wedding, but he knows there is nothing we can do at this point. She literally drank 3/4 of a 5L box of wine when she found out he was engaged. Her drinking often has her within hours go between "being thrilled to be my future mother in law" and she "knows what my whore ass is up to" and that I'm "trying to get pregnant to trap her son."