Nazir 48b - Pushing off Meis Mitzvah for Pesach

The gemara learns out from the pasuk of "achoso" that even one who is going to do the mitzvah of pesach or milah that have kareis associated with them, push off the mitzvah 'sheyesh bo kareis' to fulfill the mitzvah of burying a meis mitzvah. The Tzlach in brachos 19b is very troubled by the fact that the Rambam fails to pasken this din. The Tzlach explains that our entire sugya that has "achoso" extra works only within the opinion that a gezeira shava on one side is sufficient to prevent refutation (not exactly like tosafos who tries to make this point a machlokes r' yishmael and r' akiva). But we follow the opinion of the Rabbonon in Nidah 22b who hold that we need a gezeira shava that is mufneh on 2 tzdadim to prevent being meishiv on it. Therefore, we end up without an extra pasuk of "v'lachoso" to teach that we override the aseh sheyesh bo kareis of pesach and milah for meis mitzvah, and the result is that the mitzvah of pesach and milah which have kareis do in fact take precedence over the mitzah to bury a meis mitzvah (like the gemara thought before the extra pasuk of "v'lachoso"). Based on this the Rambam leaves out the din of meis mitzvah overriding pesach and milah, because the Rambam holds that meis mitzvah does not override pesach and milah.