I think the unrealistic dream fear about your daughter being killed due to your inaction may reflect your inability to process what may be your worst case scenario regarding custody if you leave your wife. Your wife is an intelligent woman with a bad temper and a competitive streak. Is it possible that the end of your marriage will result in the end of your relationship with your daughter? What steps can you take to prevent this from occurring? Unfortunately, as long as you are on the fence about the future of your marriage, you are unable to make decisions or take actions that will benefit you in the future. Indecisiveness always leads to anxiety. I don't really know anything about divorce or custody law but I can easily imagine that you might be better able to effect a positive outcome for yourself if you were to just quietly move forward with the goal of divorce and shared custody in mind rather than leaving yourself vulnerable by risking your wife taking action in anger if you were to take an even stronger stand on the sex issue. On the other hand, I firmly believe that taking a strong stand on the sex issue is the only way you are going to be able to save your marriage.
If there is any truth to my theory, I think taking whatever action you can in order to protect your relationship with your daughter in the event of a divorce is something you need to do in order to "differentiate". This is the equivalent of Focused Flutist having to make plans to be able to support herself in the event of divorce or my own need to improve my body image to the extent that I could confidently imagine having my sexual needs met as a single woman. I think being able to pull off the mental trick of simultaneously working towards a happy future without your spouse and working towards a happy future with your spouse is the only way to be successful, otherwise your fears for the future are overwhelming and will render you far too wimpy to take a stand.
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver