Look. The Dominion had absolutely no incentive to destroy the wormhole. Its continued existence posed no threat to them; at worst, they couldn't go through it to carry on their war effort, but it didn't do any harm to the Dominion itself. And if they could clear up the problem that kept them from going through, then it would be invaluable for their continued attempts at conquest. Destroying it would not have benefitted them in any possible way and would in fact have worked against their long-term goals.
I mean, come on, that's the whole reason Changeling Bashir took steps to make sure Starfleet couldn't
destroy the wormhole!