Given how much of the show the Dominion arc took up and how integral it became to DS9's identity I think it would feel weird if the show kept going after the war was over. Sure it would be possible to pull it off but if it only lasted another season or two, it would just feel weird. On the other hand if it went on long enough to make the Dominion War just another arc in the show then it would likely burn out before the end. Don't get me wrong, I love these characters and would love to see more of them but I think the producers made the right decision to end it when they did.