When the war is over the following will happen in short order: the Dominion will be forced back to the Gamma Quadrant; the Cardassian Empire will be occupied; the Klingon Empire will spend the next ten years recovering from the war and won't pose a serious threat to anyone. That leaves two powers to vie for control of the quadrant: the Federation and the Romulans. - Sloan, "Inter Arma Enim Silent Leges"
I always assummed that the the Federation/Romulans/Klingons would occupy Cardassia Prime and their other territory. Some sort of provisional government would be formed from Damar's resistance movement. Eventually that government would take control from the Federation/Romulan/Klingon occupation.
I guess the primary issue would be if the Federation and Romulans resume their hostilities post-war and refuse to relinquish territory they are occupying.