Well, not to get all "near-infinite number of parallel realities" on you, considering I don't think that's mentioned in relation to the Mirror Universe. But who's to say something else didn't happen to transpire in the 'wrong' direction, elsewhere in the galaxy, just by chance? Or we could go with the Butterfly Effect for a more plausible in-universe relation and ponder that one for a while.
Of course, the MU was always a separate breed from the 'Stargate SG-1 with Sam Carter citing real scientific theories' variety, so maybe nothing would happen to the Dominion because nothing is supposed to within the MU parameters.
Of course, the MU was always a separate breed from the 'Stargate SG-1 with Sam Carter citing real scientific theories' variety, so maybe nothing would happen to the Dominion because nothing is supposed to within the MU parameters.