Unlike most harem manga the harem in this one isn't maintained by misunderstandings and teenage hesitation towards confessing and starting a relationship.
So how does this end?
The Ring King (LotR) only really needs to be in a relationship with all of them until they defeat the Abyss King(?). However, they're supposed to love each other to make proper use of the rings. At best it seems like an awkward ending. To divorce everyone, tell them, "good job, thanks," and then consummate the marriage with Hime. Or Hime has a change of heart and says, "we've all worked so hard and love you and I've been selfish. We can all be your wives." and to be cheeky adds, "but I'm your first wife."
Is there any way to not have an awkward ending?