→ Spoiler
He'll go back home eventually, later that saintess will be amnesiac
Can you spoil some more lol. What happens to the duke
Later the Author will go swoop this princess & saintess. Then given choice to stay or go. The princess is dead in that Korea life, so she can/don't have much choice but to stay (she love this royal family afterall, so she's really glad that she can stay). That guy inside saintess body is still alive = so he can go back to Korea. Now then, the saintess after the guy's soul flew away, the og saintess woken up with amnesia (she didn't know practically anything that occurred since she was possessed, so she's in full-forced confusion but still originally innocently sweet). That's the small part of how they go on their lives(⌒▽⌒)
Just help that guy get back home