the cure wasn't their one and only trump card
No - using Odo as a vector was. And with Odo gone as an option, they're left with nothing, as far as directly attacking the Founders is concerned.
Fighting a conventional war with the Dominion, even with superweapons, is not going to work, as we already saw from the minor scuffle depicted in DS9 under the title "Dominion War".
And I still don't see why the Dominion would want to return to a war they knew they were going to lose?
The only reason the Dominion lost was because it fought with a tiny beachhead force (one that was backstabbed at the final hour, too). And that one nearly did in the combined forces of the Alpha Quadrant. Imagine the Dieppe raid resulting in the collapse of Nazi Germany and
Stalin's Soviet Union...
By sidestepping the annoying wormhole and simply spending seven decades sailing towards the Federation, the Dominion can deploy another such beachhead force as the first wave - followed a month later by yet another, and so on for as many months as need be. Indeed, even with Alpha in total ruins, a couple of hundred such waves will still be arriving, having left the Dominion homeland before news of the victory reached home base.
It is just as well that we never learned the terms of the treaty signed at the end of "What You Leave Behind". By all rights, it should have been a Federation unconditional surrender!