This is very interesting. My Dad died at 87 after sobering up at 80. I forgave him very early on after a religious experience I had. But we were never close and he kept the family as divided as he could. But I didn't have any pains with his passing or since. It really was a relief, and remains so. I feel so free from worrying about what he would do next. He actually died from Alzheimer's as I shared in another post. His funeral was pretty big, in his home town and many relatives cried so hard. They never knew he was a physical abuser constant drunk, they just knew his happy party side so that was hard.
My Mom, the eternal enabler, lived to 97 and she was trip to handle. She never admitted to a thing and when cornered by me she would say she was in such poor health and couldn't remember, which was just a blatant lie. She was very healthy till the day she died.
I think forgiving them both really helped ease the guilt. It's never too late to really forgive them. Forgiving is really for you, not them. I don't know if you have or not. I think counseling would be a great help as well. You are not alone.