I hear ya, I knew it was all bullshit for 10 years before I had the guts to say something to my wife. I just let my wife indoctrinate our kids and continue in it herself with as much support as I could stomach. I even attended the meetings for a couple of years toward the end just to hold our marriage together. After I talked to her and we were out (lots more detail than I will go into on this post) she confided that she had serious doubts about the time I stopped going to meetings....I missed an opportunity that cost us 10 years in that stupid religion and cost my two oldest kids some important developmental time. It could have cost us our family or worse. So even though your outcome was so much more tragic, I understand your feeling of guilt and shame, if not the magnitude.
That being said, while I carry that sense of responsibility, I also see that what I did whas what I believed to be the right thing at the time. To "live and let live", to show tolerance by example. But I also recognize my wifes own responsibility for her life and her decisions. While I COULD have known or seen her doubt and pursued it, I did not and felt it was wrong to tell another what they should believe. I would have even let her die with no blood, respecting that decision, even though I did not agree with it. I would not choose that based on what I know and have experienced since then but I still bear the knowledge of what I would have let happen.
Here's the thing, you do bear some responsibility for your lack of action, but your guilt is shared. Your wife made poor decisions and you did what you thought best at the time. I can not tell you how to live with that, but I can tell you that while you have a valid reason to feel the way you do, that you cannot, in fairness, be considered at fault. You did not cause her problems, you did not force her into making choices that ended so tragically. You could not have known all that would happen or undo what has been done, no one can.
You do have the opportunity to survive this, to learn from your and her mistakes and grow. Unlike what the witnesses teach, there is no perfect, you'll make more mistakes, often even after making a decision very carefully. Hang on and heal, for you, those who love you, and for all the rest of us that can use your perspective and wisdom that was hard earned. Fortunataly it sounds like you are doing just that.