I'm not sure I understand what you're getting at.
If regions are turned rogue, people will just take them back. Period. That is absolutely plain from the players' behaviour.
A rogue spawner would make this possible, but difficult. For as long as the spawner (vortex) is in a given area, the number of rogues that come out of it would make holding near-by regions difficult, and the spawn location almost impossible. Thus, a potentially large number of regions would be kept rogue via warfare with undead and monsters, allowing players to prioritize which regions to defend and to attempt to mount coalitions to contain it at its source, as opposed to a blight no one can really do anything about and which is mostly static, not granting the players any choices.
