People are attached to their CHARACTERS, only kings and dukes are attached to their fiefdoms. As long as they can take those characters and live on in a new location, no one has lost anything.
People taking their characters off sinking island A and moving them to island B & C will absolutely increase the player density there.
A new island for your character is still a new island to explore and conquer, without the devs having to make a new island which they've said a million times they're not doing.
Call it Noah's Ark, call it Atlantis, call it Numenor, there are lots of exciting ways to roleplay this with a little imagination.
A lot of players are really attached to realms they hold no significant titles in.
