First of all, I am so sorry to read of your suffering and Dak's death. I would like to write a little about what I think he might have felt, as I was also raised in the truth.
You son never knew JW were wrong. When he said no blood, he meant it and he felt he was doing the right thing.
The JWs are bloodguilty, but you are not, in my opinion. It's like over a century ago or more, when they did bloodletting, or did surgery without washing hands. They thought it was fine.
You thought it was right, and good. You always wanted the best for your sons. You may feel now as if you were unfair, but you obviously loved your son. You would never want to hurt him, in fact, you wanted the best for him. When my mom phones me each week and says that I need medication because I no longer say we are living in the last days, and when she locks me out of her house, and when she says, "Can I help you?" when I visit, that is because she thinks that is the best way. She cries a lot for me, because she believes we are in the last days.
I never doubted until a few years ago, when I saw so much injustice.
But you have to realize that your son thought he was doing what was right. So I think you need to stop beating yourself. You are a good person to accept your responsibility as a parent, but how far does that go?
I am sure your son would forgive you. I do my best to forgive my mom for treating me bad, I wished her a great vacation on Monday when she said she was leaving and not inviting me, I usually drive them to the mountains every year, not anymore.
Of course, my situation is nothing compared to yours.
The JWs do think they are doing the best for their family. I used to think exactly that. They think this life is not all there is, and they have a ton of scriptures they use.
You did what you thought was the best for him. He died thinking he did what was right.
You are a great person, I bet you are a great mom.
Hang in there.