I'm not overly sure why he wasn't just banned from the realm, but I guess this way was much more fun! 
First of all, it's his property and no one is justified to take it from him(not even the goverment).
Second, it's not possible, you'd have to force suceed him, that was next on the list but it required one lord to change duchy, but he never replied to any letters.
Madina lives by a diferent philosphy than most realms carry, the goverment isn't the boss of any landowner, they just make sure everyone in the republic is safe, and in case of war, all landowners defend each other.
Any disputes or politics is solved on personal levels, rarely via the goverment, for she wields no such power over it's citizens.
