The thing is, for every group he cheesed off, he made two or three others some very lucrative deals. The net gain of which was that everyone who mattered in the area decided to let things slide. Figure in the fact that anyone who offs a great dragon gets a ton of other great dragons anxious to get revenge (to let folks know that this will NOT be tolerated), and revenge against a great starts looking like a bad idea.
Plus, military might or no, Ghostwalker AKA Dollmaker AKA Icewing would glass a few thousand square miles of sprawl/terrain before he went down, and even a Thor shot might only piss him off. Back in the day, the Therans AKA Atlantis tossed the equivalent of three armored divisions/WMD's at him. Notably, this was the only time in recorded history that the Therans ever LOST one of their behemoths. He then snuck into the Theran capital city and murdered a dozen of the most important people in the empire a week for at least two weeks before the Therans called for a cease fire. During the down cycle of magic, Ghostwalker was the only great still active and travelling the metaplanes discovering new arcane knowledge and techniques.
There's a reason the entire council of great dragons backed away from him and Lofwyr twisted his challenge to combat to a challenge between cat's paws. No one wants to go toe to toe with Icewing.
As for renegotiation, recent events and new information probably made it advantageous. Or he may have plans for the region.