B"H
The Gemara in Pesachim says that the first Pesach is pushed off (to the second) if most of the congregation is tmei meis, but on the second Pesach, or is done even in tumah.
The question would be if Moshiach came in between the first Pesach and second Pesach (and especially if he came within 7 days of the second Pesach such that it's important to go through the full para adumah procedure), will we still do the second Pesach, even though we didn't do the first?
The Rambam, from the Gemara, gives a law that says if most of the tzibur was tamei with other tumos besides for tamei meis, but at the time of the second Pesach were mostly tamei from tmei meis (which usually is okay for the second Pesach) then they don't do the second either, since "the second is only offered when the first is offered",
but maybe Moshiach not arriving before would be considered an onus etc. or derech richoka, and maybe we would do the second one in that case?
Or maybe there are other factors involved, such as if the second Pesach is it's own Mitzvah or if it's a detail within the first Pesach, and even if it is it's own, maybe it's dependent on the first, but even if it's dependent maybe it could bidieved be independent,
Similar to the concept that even though the tefillin of the hand and they of the head are two separate Mitzvos, but the halacha says that they go together (and in some case(s) one can do one without the other (like what if someone doesn't have a head, do they still put on the hand one?)) Etc.
