The novels have Odo sendin' a message to the powers of the Alpha Quadrant that if they want to explore non-Dominion territory in the Gamma Quadrant, they can.
And some shit goes down with the Founders that leave just Odo & Laas runnin' what's left of the Great Link, too, so his word pretty much goes...
I still feel a little uneasy about Odo joining the Great Link at the end. Sure, I know that that's what he's secretly- and not so secretly- wanted since he found them at the beginning of S3 and the war is over, as is (presumably) the Dominion threat to the Alpha Quadrant, but there is not any direct reason to believe that the Dominion is going to reform itself into a less oppressive, tyrannical organization- though, of course, maybe Odo's goal is to change some of that? Sure, they got beat, maybe for the first time in their history (albeit outside their home turf) but their armies and networks are still fully intact in the GQ.