Suppose there is an halachically prescribed, commonly-practiced action, which has been demonstrated scientifically to lead to death of the action's object and/or subject with a certain low probability (assume that this probability cannot be further reduced).
What does the probability have to be for us to stop performing that action?
Is the probability even relevant?
Does the answer depend on whether the action is d'Rabanan, halacha l'Moshe mi'Sinaj, or d'Oraita?
P.S.: This is not an "anti-" or "pro-something" question. This is a sincere attempt to better understand the halachic process. Please abstain from assigning a specific mitzvah to the question, as there isn't one. Thanks.