I think it depends how much time passed after you ingested the SN. If youre still conscious theres a high probability to be saved (they will give you methileneblue (i dont really know how to say it in english) which is an anthidote). If youre unconscious since 20 mins or something like that there isnt much that can be done. So you cant really determine the chance of survival as they vary through time. If you survive though it will be clear that you tried to ctb, as SN is widely know by authorities because of many suicicdes that happened with it