Just to give an idea on what they might do on for this drama's ending (I don't know if they'll do it a bit differently than Yi San's ending).
For Yi San's ending, Deok Im (named Song Yeon in that drama) did die, but only after the king did all he could so that she would live. He didn't care what kind of medicine (western, eastern, whatever medicine) or who would be able to heal her (male doctor, female doctor, random slave, etc). He ordered whoever or whatever can heal her should come to the palace to heal her, but Deok Im/Song Yeon still died.
After her death, there was an episode where Deok Im/Song Yeon showed up in the king's dream. Then the ending was shown, it was of their childhood memories together then flash forward to their early youth of fun times.
Of course Deok Im will die here (interesting plot twist if she didn't). She will die in his arms, similar to how she was after she ran fast to meet him a few episodes before. A better more comforting ending for me would be after the king gave advice to his son (the next king), he would have a monologue on how much he loves Deok Im and how everything he is (as a great Joseon king and all his accomplishments) couldn't happen if not for her help. He will be shown in old age and greets death like a happy man. Then, just as the whole drama is about him waiting for Deok Im to say yes, we will see Deok Im in the other life/heaven waiting for him. She will say how much she has waited for him, then hug him, then say she misses him (similar to how he says he missed her after the episode 15 hug).