Theory

maybe what iruma said to clara and azz was a foreshadowing. he will go back to human world, forget about the demon world, but either azz/clara/amelie (since she know about the portal and her mother's story) will come to take him back and his memory will return

or maybe ali-san will do something to prevent iruma going back to human world. maybe there will be a confirmation of ali-san identity???

I obviously don't have any contact with the author's team, so I can't know for sure what will happen, but I have great pattern recognition plus I easily pick up on foreshadowing, so this might end up being really close to actual future events, so it's your decision if you consider this a spoiler, or not a spoiler and read it.

As a writer, I am very familiar with the "think of the wort thing that could happen, and then make it happen" rule.
Sullivan's conversation with the princess will probably take up a few chapters or be barely shown, depending on what exactly will be said. Whatever it will be, at the end of it Baal will either gain some really big and sensitive information, or Sullivan will owe him something for helping. (either "please help me, they're trying to take my grandson away" or "Iruma cannot leave Netherworld, he is connected to Derkila *somehow*"
from then, we have two possible outcomes: Iruma is detained for a longer period of time without being sent away yet, but the princess comes to say "let him out", and the Border Patrol will have to listen to her. but after that, Iruma will still be on thin ice, rumors probably spreading.
and a second option, he gets sent back to human world, possibly losing his memories. depending on what will happen with his ring and Ali, they might make him question what has happened to him. He also might find Ameri's mom and talk with her about vaguely remembering something weird. Azz and Clara decide to search for Iruma, they'll team up with Ameri, since she has more of an idea where he might be. Seeing them might make Merize and Iruma remember everything. Because of how this chapter ends, the princess might somehow help them get to the human world and look for Iruma, or do something later, once Iruma's back in the Netherworld. That scene he used Change Loki to make himself look like a demon to avoid being sucked into the human world, with how Ali/Derkila was acting like it was his plan all along (I mean the entire situation, not just the temporary appearance change.), and with that one close-up panel of happy and relieved Iruma looked when he got back, when his teeth still haven't yet fully gone back to normal, and how he shouted moments before that he wants to be a demon- yeah, he's probably not gonna be fully human at the end of the series. whether that be through whatever connection he has formed with Ali at the beginning of the series, him being a descendand or reincarnation of Derkila all along, or through how exactly he interacted with the Netherworld, we know now that he's not exactly like any other human anymore - if he was, he would probably be already starting to get sick like Merize. I don't think a full transformation will happen until the very end of the series, if at all, since we don't really know what exactly could that look like. He could either somehow already be part-demon, somehow fuse with Derkila, or we could discover that demons are actually mutated humans or something, and he is already starting to turn into one because of giving into his greed? but whatever it turns out to be, it's probably gonna take some time to fully develop and get used to. and rumors about him being human might still be going around.
I understand that some fans might not be happy with this, but with his identity as a human being revealed, there were going to be massive changes to the story moving forward anyway. being partially demon might make it more interesting if everyone knows. he would have to navigate getting used to how his body now works, avoiding potential attacks, how people percieve him, and how he stops being human just after telling Clara and Azz makes the entire thing a bit awkward.

but who knows, maybe something completely different will happen. like us waking up to find out it was all just a bad dream and everyone is still happy and together