The Founders believe they've found the Progenitor, which turns out to be a giant planet-sized Changeling. There's a lot of hope and expectation for the future of the Link. Unfortunately, by the time Odo, Laas, and some of the Link get to it it's dead - murdered in fact by an apparent rival species gaining power in the Gamma Quadrant.
This turns the Great Link's joyous expectation into an incredible depression. Not quite suicidal, but the Link breaks up and goes their separate ways, overcome with hopelessness for their future - and guilt about what happened to some of the Hundred and to the Progenitor (they blame themselves for their god's death). They no longer care about the Vorta, the Jeh'Hadar, or the Dominion at all - they've basically given up.
What this means is Odo and Laas are left as the sole rulers of the Dominion.