Molly is the logical candidate for Harry, if she became mortal again. However, I have a feeling that while Harry is getting himself out of the Winter Knight's job, Molly will make the choice to remain an immortal. It's mostly just a feeling, but Molly has said that her work as the Winter Lady is important. I can't picture Molly running away from her responsibilities unless there was someone ready to jump into her current position. I suppose Lea could do the job, but that doesn't feel right to me either. (Even if I ignore the possible virginity element to the job.)
I have feeling Faerie Courts shall be destroyed by end of BAT, so while Molly will survive - mantle of Winter Lady shall not. (Nor Mothers nor Mab).
And that will also of course free Harry from Winter Knight.
No Winter Court, no Winter Court responsibilities.
Black Court of Vampires shall be blackmailed (sic!) to guard Outer Gates in new age, so they shall get a free hand in robbing graveyards from bodies, but won't be able to prey on mankind as much
One question is will Harry ever be mature enough to have a decent relationship with any woman?
By that, I mean there was an element of "mommy" in both Susan and Murphy. There is a part of Harry that wants to be mothered, perhaps because he never had one, and the "sage" advice both women gave Harry filled that void.
Was it with Susan? I had a feeling she was quite a dummy at least in first trilogy. (I'd say that could definitely be a thing with Luccio though).
But then Dresden's lifestyle so far never sort of lead to him having relationship beyond dating, that's another question. (Which is another reason I wished Mursden was longer a thing.)
With the WK gig going to Thomas or Toot Toot
Within current rules Toot Toot cannot become WK