Maybe I misunderstand you. What I think you are saying is that as long as all players update to the same patch then the game will still be playable.
I'm not very technical with these things but this is the way I understand it ... if we all upgrade to the new patch, when you try to load a PBEM save that was saved under the old patch, even if the game loads at all, once the game progresses to an item that has changed with the new patch, the game will crash. I know of no way to update a PBEM save to work with a new patch.
Like I have said, it is possible that, with current programming abilities, things have moved past those old problems that I talk about, and if that is the case then could someone please speak up and state this. Failing this, I fear that the PBEM may not work with the new patch.