Yevamos 121a - Mayim She'ein Lahem Sof

R' Moshe (E.H. 1:41) was asked about a Talmid Chacham who was missing in the Holocaust, and three years have already passed that they haven't heard from him. Can his wife remarry? He begins the discussion by pointing out what i posted yesterday that there seems to be 2 possible justifications for the chumra of mayim she'ein lahem sof: 1. to be concerned for a mi'ut that is common. 2. a stringency bec. of the chumrah of eishes ish. He explains that both are really true. The fact that most people would have been killed in that situation is a "rov", but there is a mi'ut hamatzuy of people who survive. However, once there is substantial time that passes and we still have not heard anything from him, there is not even a mi'ut hamatzuy to be concerned about, so the only rationale to maintain the issur even after time has passed is because a chumrah of eishes ish. Based on this he explains the rationale for the amoraim for holding that a more famous person (such as a Talmid Chacham) was not included in the gezeira of mayim sh'ein lahem sof. Originially they only made an issur in a case of mi'ut hamatzuy, but didn't want to change the pesak by a regular person based on how long he was missing, so by a regular person the issur was applicable and not removed even if it turned into a mi'ut she'eino matzuy. But, a famous person who we have not heard from, and if he is alive we would have heard right away, they originally considered a miuty sh'eino matzuy and therefore did not make an issur just because of the chumrah of eishes ish. However, the gemara concludes that even by a famous person we begin at the first moment with a mi'ut hamatzuy since is being out of touch could be attributed to many valid explanations, and therefore they imposed an issur even in this case. His point is to develop a yesod that chazal only use the chumra of eishes ish to extend a situation that begins with mi'ut hamatzuy, but if the situation begins as a mi'ut she'eino matzuy, the chumrah of eishes ish is not a compelling enough reason to be concerned for the mi'ut sheino matzuy.