There’s only one way to find out: ask. Your husband needs to sit down with his son and ask. He should leave anger and defensiveness at the door and be prepared to really listen.
Are there things he’s going to be confronted with that would crush his soul? Probably. As someone who has been both the estranged child and a mother whose two oldest sons were beginning to estrange, I know this isn’t easy but if both sides are willing to do the work, it can be resolved.
I wish nothing but peace, love, and happiness go your family.