Much of the dissapointment of closing an island comes from the loss of status and power currently held by a charecter. Not only that, but to keep playing you now have to move to an other island where others already hold dominance. A more attractive option, at least to me, would be seeing a continent wiped out, but a fresh one start at the same time. It might not guarantee your previous influence, but at least nobody starts above you.
I did not read the whole thread, so I don't know if this was already suggested or disapproved of (in such a case, my apologies), but why not close two islands, for example Atamara and Beluterra, and then create a new world using the old map. You could even go so far as to make the starter realms correspond to some of the stuff from the both islands, so people can try keep their culture alive, though I think that might just be raping the histories of both continents.
I also like the idea of holding multiple titles, but I doubt it would ever happen in practice, especially if there is penalties to productivity. A monarch would probably not want dukes with several duchies, and a duke would not want his lords to be inefficient. And since they are the ones calling the shots, the power would stay distributed if possible.
Freezing an island, much like blightning regions, will serve as an eternal reminder of things lost, but I would not have anything against either. I'll keep playing anyway.
