Maybe but maybe not. Someone here predicted (I think early this year) that the series might end at chapter 666 and that's possible. This is a major arc for sure but there seems to be lots of open/unexplored plots and characters:
- Sullivan's curse backstory (aka why he can't be demon king) and why he took Iruma to demon world
- why the ring has Delkira's mana (might be resolved in this arc)
- why Iruma doesn't get sick like Merize (pointed out by one of the fans here)
- what happened to the missing 13 crowns (we only know what happened to one of them)
- the next king (if it's going to be Iruma) handling the publicity afterwards and his eventual coronation
There's more that other fans theorized but I can't remember all of them on top of my head.
Maybe there will be an end to the school arc, like they have told us before that the normal max level they get at school is 6, Iruma is 5.5 only because other people didn't let him get 6, now to get stronger and get more followers (to eventually become demon king) he needs to travel the demon world and change it from inside.
Maybe it will be like tokyo ghoul and we will get a Mairimashita! Iruma- kun "re:"
It can be like Naruto Shippuden leaving school behind and traveling with a sensei (Mephistopheles) and getting levels up (like medals from pokemon) from weird powerful demons living in a cave(like the deities )or demon generals( like the three heroes)
huh. im kinda wondering are we close to an ending? one of the biggest plot conflicts is going to be resolved soon with this arc, so im wondering if there would be more to follow or are we also going to find out the connection bet. iruma, ali, and delkira in this arc too?