Realistically the only thing they own is limited in scope and not worth much at all. The background of the Realm storyline wise is practically it.
There's not much that's original thought. The enemies in the game are very generic and just basically a staple of mmos. Same goes for the weapons and spells etc.
Really the only things I can see as retainable would be the background storyline, the pantheon of Gods/Goddesses, and possibly the town names.
All of which could easily be circumvented with some clever writing and still be able to be a solid spiritual successor and possibly even be a good continuation of the storylines.
I'd already thought of multiple ways to accomplish that and still have it feel like Realm with new places and Gods/Goddesses, just takes some creativity.