Actually... If Sidious hadn't been defeated, his massive navy and elite troopers would have been ready for the Vong invasion. The death star would have been VERY convenient to have around to blow their moving home world away
It was a very long time ago, so I won't be able to find the post, but someone pointed out that everything Sidious was doing before the Rebel Alliance appeared, was preparing for something. This person provided even more evidence that the thing Sidious was preparing for was indeed the Vong invasion. Why would you build a massive station capable destroying planets (Which the Vong planet doubled as their primary base), without anyone to fight? Sidious didn't need the death star to end the clone wars, and he knew that. He wasn't expecting the Rebels to appear either, so the death star was not built to fight an insurgency.