I am going through something similar....just separated from my husband of 14 years, in a mentally/emotionally/verbally abusive relationship....
And I dread the loss that I am facing with his family - especially his son. He is in an adult in the military and just got married. We care about each other, and I know he wants me to still be a part of his life - since I've been in his life since he was 6 years old and he's now almost 22....and we have a great relationship. But it won't be the same. I won't be a grandmother to his children.
I can relate to your loss, and it is overwhelming. It's bad enough to have to endure the emotions of the marital relationship ending. Losing more family on top of that is just too much to handle.