The Onus For אונס Regarding ע"ז

We discussed earlier in the week the miseras nefesh of Channenya, Mishael and Ezaria learnt from the frogs.  We cited the opinion of Tosfos that it wasn’t avodah zarah.  Another prove of the Tosfos is from the Gemorah in Ketubot (33b) that says if the authorities had tortured Channenya, Mishael and Ezaria then they would have bowed down to the statue.  How could they bow down to avodah zarah?  It must be that it wasn’t a real avodah zarah and they gave up their lives because it appeared to look like avodah zarah (see Tosfos Rosh, Rashba in Ketubot.)  However, the Rambam is of the opinion that one may not give up his/her life if one isn’t obligated (see Yesodah Hatorah Ch. 5.)  If that is the case how could Channenya, Mishael and Ezaria be willing to sacrifice their lives?  

I have seen a few Achronim giving different answers.  However, the Rambam says explicitly in law 4 that Channenya, Mishael and Ezaria are examples of those that were mekadesh shem shemayim b’rabim by not serving avodah zarah.  It is clear that he holds it was a real avodah zarah.  In that case the Rambam must hold of a different answer to the question of Tosfos.  It could be that in Pesachim he understands like the second approach of Tosfos that Channenya, Mishael and Ezaria had the option of running away and then learned from the frogs to jump into the fire and not run away (see the midrash in Shir Hashirim Ch. 7 verse 8.)  This idea of Tosfos is quite difficult, if one can run away and not give up his life, why not do that?  See Shevus Yaakov volume 2 #107  ואכמ"ל.)  However, we still need to explain the Gemorah in Ketubot?  

There is an opinion cited in the Shita Mikubetzes in the name of Rebbe Eliezer that one must give up their life not to serve avodah zarah, but one doesn’t have be tortured which is a worse.  It is clear that this opinion holds that the law that one must give up their life for avodah zarah isn’t a removal of the petur ones, it just raises the bar of chiuv to extend even to give up your life, however, that doesn’t extend to torture.  According to Tosfos, there is no difference for the חיוב של בכל נפשך  is a הפקעה  on the petur ones.  According to Rambam it obviously isn’t a הפקעה  on the petur ones for he holds if one violated and didn’t give up his life instead of serving avodah zarah, there is no punishment for the individual.  The individual was מבטל  a מצות עשה של ונקדשתי , but it still was a situation of ones so there is no punishment administered.  However, Tosfos Avodah Zarah (54a) disagrees and holds one is held culpable even באונס.  Tosfos is לשיטתו  that there is no exemption of  אונס when one must give up his/her life.  Based upon this, the Rambam can hold like the Shita and that’s why Channenya, Mishael and Ezaria would have bowed to the avodah zarah if they were under torture.  The צ"ע  is why is this law not cited in Rambam?