I can't see them resolve this until 5.3, though I have this odd feeling that Thancred might stay behind for Ryne, or his source body started to decay since he was the first to be "ported" over... I feel his "arc" is done after we finish with Eden. Heck, he's and Urianger are part of the Eden arc but I can see Urianger bow out and it's just Thancred, Ryne and the mystery woman that we haven't seen yet.

OR

Everyone gets to go back, even Ryne gets to move over to the Source with us and play a much LARGER part of the overall XIV story since she has that gift of hers.