Rashi asks that according to reb shimon which holds that Davar she'Eino Miskavein is Mutar why is it Mutar but since there will for sure be an opening it should be Asur? so rashi answers that it's possible to do it in a way that there Will be no opening. My question is that the gemara says before hand l'Dam Hu Tzarich O l'Pesach Hu Tzarich and the gemara also says v'Im Timtza Lomar l'Dam Hu Tzarich u'Pesach Memeila Ka'asi .... so we see clearly from the gemara that we are speaking about when an opening happens so if so how could rashi answer that it's not a pesik reisha over here because he can do it in a way that no opening will come about but the gemara us speaking about when an opening will come about
Benzi, London
It would seem from this that Rashi maintains that if there is a way to perform the act without transgressing an Isur, even if he does not know whether he will manage to perform in that way, it is not a Pesik Reisha if that outcome is not absolutely certain. In this case, since there are some who are Baki and will not remove blood or make a Pesach, even if this is not his express intention, it is not a Pesik Reisha. This is the conclusion of the Acharonim in Rashi, even though it would seem to contradict his opinion in other places in Shas.
The Gemara's "Im Timtzi Lomar" does not mean that there must be a Pesach but rather that it is possible that there will be a Pesach (since it is still possible that Dam Mifkad Pakid and there will not be a Pesach), so this fits Rashi's thesis that if it is not certain that there will be a Pesach, even if it does happen it is not a Pesik Reisha.
Yoel Domb