I know that it's been theorized by some (not sure about WoJ) that the binding Maggie put on Raith is now anchored to Maggie Jr as well because of the nature of the spell. I suspect the spell doesn't work like that. It's anchored to Harry, and Thomas, no one else.
So here is where I think Mirror Mirror causes the issues. I believe with Thomas locked on DR he is no longer feeding the spell. Harry placed him there to protect him from magical attack, and it would make sense that he'd no longer be fueling the spell. If he were, then powerful beings on DR could reach out from there, and I don't believe they can. Then in Mirror Mirror Harry will be pulled into another reality. I think this will be enough to severe his connection to the binding. With Harry, and Thomas no longer fueling the binding, it will lose power very quickly, and Lord Raith will be able to feed again.
I believe that when Harry makes his return from the alternate reality he will find that Lord Raith killed probably at least a couple of dozen of women. Feeding heavily, and refilling his gas tank. Lara will once again be submissive to him, and he will have taken control of the White Court.
This will create a major problem for Dresden. His marriage into the White Court will mean he must respect certain laws, and in some ways be obliged to do what he's told by the leader of the Court, Lord Raith. Harry will once again be in a really horrible position, just where Jim wants him.