Legally speaking you probably have a point. However, Astrum doesn't see it that way, and making this argument would require Asylon to be willing to back up such a claim. I would be surprised if they were. They've already benefited immensely from this turn of events (although having Allison as a new neighbor may come back to haunt them), so it's really not in their interest to sour relations with Astrum and Kabrinskia over a couple of regions that they were willing to sign away to Terran in the first place.
Any claim by ex-caerwyns would require the other local realms to acknowledge them. So really it all depends on if Caerwyn becomes a distant irrelevant memory to the remaining realms. Now I'm all the way over in the East, but from what I see most realms have moved on and Caerwyn is largely fogotten.
