You cannot possibly imagine that who Hilgya is, and what motivates her, is not pertinent to Durkon’s arc. Durkon’s mantra is to do what is right, especially if it makes him unhappy, including marry Hilgya; ergo, her part in the story is not done. I credit you with having the intelligence to tell the difference between liking the character and detecting that her narrative role is not complete.
If you could just point me to the part where I said this is about caring for Hilgya, that’s be great. I don’t remember saying any part of your strawman except “Hilgya.”
This is about what I think is likely, vis a vis Hilgya’s abrupt departure.