hmmm i think it's not Alikred but the "dimension" itself or the portal may be.
I do wonder.
It could be that Alikred had more memories of when he was (probably) the demon king while he was in the portal, but knew he would forget when he left, so the see ya later was referring to when he gets his memory back?
I would also have assumed we would know by now if Alikred was gone.
I also don't know whether if Ali was gone, Iruma would still have magic. I am unsure whether Solomon's ring is a real thing that Ali is attached to, or that Solomon's ring is something grandad referred to, but his ring isn't actually that.
Especially since the magic doesn't come from Ali, but is from the grandad and Ali just consumed it. He was still able to do magic when Ali went dormant as well
With the summer break arc coming to a close, I feel like Iruma will have a problem in a future arc that involves using magic. Since when he came out of the gate we see something that says "see ya later" which I'm thinking could be Alikred. It would be really problematic for Iruma if it turns out that he can't use magic anymore..