Maybe it was the wrong thing to do, but when I left my XAH, I never told him it was because of his drinking. I never talked to him about it, I never complained or asked him to stop.
He begged me for a reason why I was leaving and I just said that I didn't want to live my life this way anymore, I didn't love him anymore, and I wanted to move on with my life. He KNEW why I was leaving. I wanted him to admit it, at least to himself.
Your husband could make the effort, but it probably won't come to anything. Unless he wants to explain the consequences of her continued drinking - boundaries that may include no contact with the family unless/until she's sober and working a program - then that's on the table and she can do what she wants with the info.