Hi there ! If you have writers block, I have a idea. Beware I am a sucker for bad / sad endings.
See - Haemin was supposed to die the day y/n went into her body. Now to go back, Haemin has to die. How she knows ? She had a dream that told her that and the fact that she must die before her 4 th birthday or any birthday ( your choice ). On her fourth birthday ( based on what my mind cooked up ) a hater tries to shoot our hope but because Haemin is in his arms, she gets shot ! Now you can decide if she dies quickly or painfully like coma to recovery to infection on the wound to death.
and in our life nothing changed, we are the same. Like 2 bodies share same mind. She reacts to Haemin etc etc
So yeah !
P.S - after death,if you follow this, the bangtan gets some shot letters from Haemin in which she tell how much she loves them !