That only damages the residence when you return to the campaign map. It does not destroy it. And yes, flaming onagers are fun. Too bad burning buildings don't kill population or units standing next to them. There should at least be a morale penalty applied against units in the city for all the smoke and chaos caused by my bombardment. And archers should be able to do the same thing too with flaming arrows. Too bad the trajectory of the missiles is not as high as it was in MTW, even after v1.2 patch. Most of the friendly fire problems in RTW are probably due to it being too flat.

Are the indestructible buildings hardcoded? I see nothing in the buildings desc files to specify whether a structure can be demolished on the campaign map.