I hope this doesn't turn into too much of a t/j, but I'm with you on this. If I'm perfectly honest, I still do expect an apology someday... but by someday, I mean, like, years and years and years down the road, possibly.
The way I figure it is that a lot of this is contingent. It's contingent on them figuring themselves out... if they ever do the work. I doubt my X will unless something (else?) catastrophic happens in his life (like he gets fired, someone cheats on him). In that case, a version of an apology might be something along the lines of an email that basically says "oh... I understand why you hate me now. I'm a total shit."
The sad NPD version of that would be if the bunnies and rainbows die and he starts to panic that he's alone. Then I might get an apology if he thinks it could somehow get me to sign up to be his babysitter again.
But more likely I think he may get to a point when he is an old man where he might look back and realize that we had a good M and I was a genuine partner with whom he could have had a nice life. In that case, experience and just the passage of time may reveal to him that he was a shit.
This may be a little loopy or sadistic on my part, but one of the reasons I NC/S/D so quickly was because I wanted out of there while I still had some dignity left so that I could be preserved in his mind as someone who was strong and decent until the end. One of the reasons I maintain NC now is because I want him to only have memories of me as the nice and loving girl he M... so it can haunt him, if he thinks about me at all.
But, anyway, in none of these scenarios is an apology coming because he's a genuine or good person. Because a genuine and good person wouldn't do the things that these WW do.