Let's see, ....
The Dominion are about to totally vanquish the Federation, when they begin to keel over and die. When the dust settles, we discover they have all died from a severe case of the common cold.
Or ...
The Dominion are about to blast Earth out of its orbit, when suddenly they surrender. As they are leaving to go back to the Gamma Quadrant, one of them turns to Sisko and says, "You have a hole in your mind."
Or ...
While the Dominion are shooting everything to bits, they suddenly turn back to defend the heart of their territory from a group of aliens who want to build a supergalactic highway through the heart of the Gamma Quadrant.
Or ...
The Federation is losing badly. Then, archeologists exporing caves on Vulcan discover an Oracle which suddenly comes to life with the visage of an ancient who's name is Harry Seldon, who tells the Federation how to defeat the Dominion.
Or ...
While the Federation is battling the Dominion, a lone Ferengi who has been exiled by his compatriots for not being profitable enough, comes across a strange little ring with a strange inscription inside.
Or ...
The Dominion destroys DS9 and occupies Bajor. Jake Sisko escapes to the great deserts and learns to ride the bajoran sandworms...
Or ...
The Organians come along and make everyone put down their weapons...