I fail to see it. If the Empire had won, you would have had a power struggle between Vader and Sidious, and it would probably resemble the infighting of the Imperial Remnant, the Yuuzhan Vong woulda still showed up a few decades later, which would have given the Empire a common enemy after they get their asses handed to 'em for the first half of the war (and I get this feeling Sidious woulda set up Vader's death at the Vong's hands during this period) before the tide turns in favor of the Empire, running the Vong out of the galaxy. And then the power struggles would resume again.
... and the only difference would be a Death Star, but for how long that structure would last is unknown (kinda like its significance)....