Maybe I missed a turn here but I don't think anyone was advocating secret rolls when dealing with life and death... really I'm just going to use them on those occasional unknown unknowns kinda rolls.
As for the insta-death roll, it's going to happen at some point but character death is never the result of one roll. It's always a series of actions and roll(s) that lead to that last one, so for me I'd go with it and let the character die. It's happened to me and I only needed a few months of therapy. I guess though it might be best only to play with people that have insurance...
At least a few people have said all rolls are hidden when the DM. In the past all my rolls were hidden behind the screen. I've learned with this system and watching new GMs on the interwebs that this isn't necessarily the best way to do things.