Starksy..great question to which I don't have an answer. Let's say that the M got to the point of being "perfect", or at least "amazing". Big if. Do i need an apology or just knowing that my M is back is enough? not sure right now. Need to digest that.
And again, please don't misunderstand -- I'm not saying you should or you shouldn't, and many never do get any sort of stated remorse. From my experience and observation, I also don't think it's even necessary for a successful reconciliation.
I do, however, think it's necessary that BOTH spouses "get" what it was that got them to the abyss, go through the requisite introspection and self-improvement, and demonstrate to one another some sort of "Hey, I hear you and I get it" type of thing that shows that they really DO "get it."
I'm really just trying to get you to start thinking about this ahead of time. Because -- like affairs themselves being "dealbreakers" or not -- if stated remorse is NOT something you need to heal, you shouldn't push for it as it'll only unnecessarily make you look needy and/or "lording it over" her.