It's honestly hard to say for now, we don't have anything to go off of considering the floor we've already seen involved already dead people. I'd say that ideally what'll happen after Silverlily, Gong-ja, and Heretical Inquisitor leave is that the story will transform into a more straightforward romance novel, with the Gold lady being wed to the Crown Prince and the butler simply pining for her from a distance.
(spoiler)
Raviel stays! And there is a way to travel between worlds so Gong ja will meet her from time to time. [(Their regression also interconnects, not sure if it's mentioned in the latest manhwa yet.), ex. If gong ja dies, Raviel also regresses.]
*Spoiler*
Butler will not be able to remain cause he also made a wish using his life/soul as collateral with another constellation. That is also why none of the people there remember the Butler’s name, even Lady Golden Flower that is his childhood friend. Gong ja will reveal what his wish is and why he made it on the day of his wedding aka. battle of this arc.
But what happens when gong-ja succeeds and returns to their world, would the butler remain or..