I'll mention T'ra Saa again, who's showing with Battle Meditation allowed a near-complete evacuation of a besieged location against a superior force to get out with it's forces mostly intact. It had been intended to be a trap to wipe out the Galactic Alliance Core Fleet and the Jedi and a good portion of the Fel Empire's forces in one go, but due to her powers they made it free.
Yet the ROTJ novel states that it was the Emperor's death that threw the dark side and, consequently, imperial forces into disarray. Declann is irrelevant.