My thoughts would be that the death star would be a way to insure the populations loyalty. By making a demonstration of imperial power it could hinder the ammount of planets willing to give aid to the rebel cause for fear of retribution by the empire. In return destroying the death star would give the populace a reason to not fear the imperial's and rise up providing the rebels with acess to new bases, technology, weapons, ect. Look at it as a two way street destroying the death star would give the rebels a much needed propoganda boost while keeping the death star in service would hinder the rebels ability to effectivly combat the imperial fleet. Just my thoughts on the matter.