What if Odo was able to save that changeling baby?
Section 31 quickly kidnaps the baby and uses it as pawn to negotiate a treaty with the Founders. The changeling baby, being the first infant to be discovered in a millennium, is more important to the Founders than the Alpha Quadrant and Odo combined. The Dominion agrees to a non-aggression pact with the Federation and the Klingon.
Odo remains a solid, and eventually marries Kira. Sisko is still tasked with the mission of destroying the Pah'Raith, but is asked to do so much earlier than if the war had broken out. Sisko succeeds and becomes a Prophet. As a prophet, Sisko was essentially in control of the worm hole and he would wipe out every Dominion warship and convoy that attempts to come through. The war never happens.
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What if Sisko was able to dispose of Dukat int he caves of fire without having to sacrifice his own life? (Meaning Sisko lived as a corporeal being while Dukat was vaporized.)