Q. You mentioned (question 3038) that if one is engaged in the mitzva of Hatzalat Nefashot (saving lives) and mistakenly, without any irresponsible oversight, remiss or negligence, and due to reasons beyond one's control causes the demise of the patient one is trying to save, he/she is not held responsible and liable to galut (exile) as a rotzeach beshogeg, (one who accidentally kills another person) is, does that apply to other mitzvos too?
A. Indeed it does, but it also depends on the situation and other factors that can affect the outcome.
About 15 years ago a Monsey butcher was accused of selling non-kosher chicken as kosher, leading unsuspecting shoppers to commit a grave sin by ingesting meat that is metameh or makes one's neshama and mind impure. Some buyers were elderly Holocaust survivors, that even during the war starved and refused to eat treif meat, they were now very stricken and affected. Rabbonim at the time tried to placate and calm them by expressing that if they were tricked and did not have to suspect anything, the ruach hatumah or spirit of impurity is not created and does not affect them. This is based on the Ponim Meiros responsa (2: 41) that compares it to a Korban Pesach that was permissibly shechted on Shabbos (as will be with Hashem's help this year) and when eviscerated it turned out to be treif. The rule is (Peshachim) that although the owner did not comply with the mitzva of Korban Pesach, he also did not desecrate Shabbos and does not have to bring a Korban Chatos since it was eaten, as you pointed out, without any irresponsible oversight, remiss or negligence.
Just to mention another case. Chelkas Yaakov (O.H. 16) addresses the shaila of someone acquiring a very good pair of tefilin from a respectable and known soffer. After over three years, when they are checked, they found that one parsha of the Shel Rosh (the head tefilin) was missing. He rules that the wearer is not considered responsible, since he followed all necessary requirements.
When I questioned Horav Shlomo Miller Shlit'a if the principle of 'Choshav odom laasos mitzva,' If a person was planing to perform a mitzva and by accident or force majeure was unable to carry it out, it is considered as he actually complied with it. (Kidushin 40a), the Rov replied that it is so indeed, and would apply also to one trying to save lives, as in the question above.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit'a