And so, the other fear comes out.
I mean, from the moment we heard that Delkira vanished, and that the class is the "13 Misfits" (i.e. a mirror of 13 crowns), it was pretty obvious plot one could choose to have Iruma vanish at one point too. However I think it will happen when
1)Sullivan is occupied or otherwise indisposed
2)During a summer break chapter so the class isn't occupied either (I can see Kalego giving being pissed at the class for not paying attention and giving a motivational speech to them to either trust the demons searching for him or do something about it, but it would be pushing)
3)I'd see it after we're more close to the og 13 crowns (by the way of either Iruma, misfits or the 2 other contestants interacting with them in comic outside the whole "Demon King" stuff, we already have characters like Ameri's dad or Alice's mom for which it would feel natural, but most of them are still strangers as characters go), so the chapters could explore and contrast their reactions to Delkira missing