I just realized, in part due to some other poster who shall not be named, but: if Sisko had taken out the Negh'Var, he probably would've killed Martok and Gowron. Two things would then happen: the remnants of the Klingon fleet would attack en masse and surely devastate, if not outright destroy, the station; or the Klingons retreat and full-scale war occurs, further weakening the Alpha Quadrant against the Dominion.