I'm happy to move this to my own thread if it's better suited there, but I wanted to chime in as someone who has similar stats (BD 2011/D 2013/M to OW 2015) and sought a lot of data in the same way over the years.
1) Is marriage to the affair partner more likely in an MLC situation than a typical affair?
I've not seen anything that confirms this, but it does seem as our membership has grown here, more MLCers have married their OPs. That's just going on what I've sensed from reading story threads, not any numbers I've tallied. There are more children being born of the unions, too. All of that may just be because there's a bigger sample of people from when I first came here in 2012.
2) Are there any known instances of someone marrying the OW/OM and then divorcing them later?
It's complicated.
From MLCers whose spouses are on this forum? I can't think of any who have divorced the alienators once they are married to them. In real life, there are certainly examples, but they usually lead to more marriages to other people, not a return to an LBS. I do know one man in my industry who shared his story with me back in 2011. He left his wife and kids for another woman, had kids with her, then later divorced and remarried his first wife (they're still together, running a business and very happy. He'd told me his wife had been a stander, and it was never an issue to remarry, but the kids from the first marriage were a tougher hill to climb. He said he expected winning back their respect was going to be his life's work). But that sample of one has not in any way mirrored my experience. I still find it to be a beacon of hope for how good people can find their way back to not just their families, but to themselves.
To further complicate the answer about divorce and the forum though, there are LBSs here who were either the affair partners or second marriages without affair being present who have seen their spouse return to the first marriage. Should those numbers count toward divorcing an alienator or marriage reconciliation? And none of what I'm saying is to place judgment on anyone, I'm strictly talking for numbers. How deep of a covenant keeper a person is may play in to how you view the situation. A two-year first marriage, then a 30 year second marriage, that then goes back to the original spouse, may be a dream reconciliation story to a committed covenant keeper, or just another crazy symptom of MLC to an LBS who is not a CK.
This is where the longer past BD we go, the less the statistics really paint any pictures for us, but the fine details of our individual situations do, I think.
In my case, my xH found someone who was also married and had the same problems he has, they have a crazy life that is likely bonded by mental health issues, financial problems, job loss, family issues, addiction and an off the charts dependency on social media and tech that keeps them distracted from working on themselves in any sort of healthy way. Their "happiness" and "love" is relative to all of those things, and certainly, they have a lot in common that could make it complicated should they ever wish to separate. He would in no way be a match for me at this point, and I have no desire to gloss over all that has happened to me because of this episode in his life (though I stood for over 5 years initially, even after the divorce), so I don't really need to disqualify any happiness he may be having. It still sucks that this happened and there is a lack of justice that someone can just blow up a marriage and life goes on. But taking focus off of that is really the only key to getting past it, because that fact is not going to change. Even if they came back and wanted to atone, it wouldn't take away that it happened. So all we can do is heal, no matter what.