Luke would still be watching the space battle from the throne room, only he would be watching it from Coruscant. Palps would still be in command of the DS. The DS would be in Coruscant's orbit, blowing rebel ships away.
Picture that "Luke obsererves the space battle" scene with little shapes and small flashes. Now imagine that with a distant DS2 in the same shot.
You really wouldn't have to edit much at all, just add the DS in a few shots and Coruscant in a few.