I think there must be another way. If I remember correctly, his mother "decided" to reincarnate. I assume she was able to not do that if she wanted to. I believe that's why Jaeshin hates his mother, cause she could've NOT leave him.
Also, Jaeshin wanted to take Lee Nok to hell with him, so he should've had something in mind; and what Jaeshin was thinking of doing, probably was possible after Lee Nok's death, that's why Jashin's brothers warned him not to do anything stupid since they said "Lee Nok will die soon anyway".
Somehow I'm sure there is a way, but unfortunately, I don't think they use It. Actually, I think the opposite might happen. I guess instead of Lee Nok becoming a ghost, Jaeshin might become completely human (if we are going to have a happy ending, of course).
We never know, Jaeshin might be able to reincarnate too, since he is a mixed blod.
Call me crazy, but somehow, I don't mind Lee Nok becoming a happy ghost and leaving with Jaeshin ( ̄へ ̄)
I mean, he is already living in hell. He is strong and hard working, and he is always trying his best, but if he dies, he won't lose anything. This world would lose a persious person that could've saved it. We can't forget the fact that he is surrounded by trash beings and is suffering his whole life. I don't care about people around him. He doesn't need to suffer more to undo the devil queen's deeds for the sake of the country or any shit like that... He deserves a lot of love, affection, and time for himself to do what he likes to do in peace; without fearing of making the stupid king furious or running from to the devil queen's tortures, and I think it may be hard to find that peace in this world considering his circumstances. Although if he dies, it would be something the devil queen fears the most, so that's another good point for it, though it still breaks my heart. ( T﹏T )