Now that everyone understands what exile does and does not do, I expect (hope, really) that when it is used, it's used on people who can't afford to wait it out or aren't prone to griefing. Example: Malus was going to use it on those people from the Huntsmen of Noble Right, but then I read the details and sized up the will of the competition and wrote it off as suicidal.
Doesn't really sound like a worthwhile option then.
Other than a self destructive exile attempt, what else could a ruler, or anyone for that matter, do against a duke?
I am, unfortunately, unlearned in the Lurian arts...this forum post woul be a good place to list alternatives since exile proved bust