The best mod I know so far that does such a job and it's very useful when you have a lot of mods especially those which add new & stronger enemies\battles etc so that important character don't die(but can still be killed by you) and you don't lose anything important with almost no compatibility issues with most mods.
Note: I'm using it with the current Early Alpha of SPM 5 & I have encountered no problems so far without needing to edit anything even among load order(I just put it at last).
Link: https://www.nexusmods.com/skyrim/mods/84394/