Well, thanks to the magic of iMovie and the ability to guard my children's eyes from the outrageous Princess Leia slave costume, my children were initiated into Return of the Jedi a few months ago (after asking me for years when they could see the conclusion of the trilogy). Re-watching it with them, I was reminded of the rather abrupt end to the Battle of Endor.
I always wondered where the heck the entire Imperial fleet vanished to after the Death Star blew up. It's pretty obvious from the film that they still heavily outnumbered the rebels and could have easily crushed their puny fleet.
But as I thought about it some more, aside from how fast they took off, it's not totally crazy. Morale and leadership is a huge part of warfare and there are countless episodes in history where vastly superior forces managed to snatch defeat from the jaws of victory because they basically wimped out. Off the top of my head, the most obvious example I can think of is almost any battle of the War of 1812. Take the capture of Fort Detroit, for example. Sir Isaac Brock on the Canadian side had about 1000 troops, only 300 of whom were regulars. The American fort was garrisoned by 600 regulars and close to another 2,000 militia. But by being bold and preying on the fear that the American general had of the Indians, Brock took the fort with only two wounded. Even the Battle of Queenston Heights, where Sir Isaac Brock was killed early in the fighting, ended up a British/Canadian victory due to the timidity of the American generals.
So, when we consider that the Imperials just watched their prized flagship blow up (for unknown reasons -- no idea how the bridge blowing up would suddenly make it fly into the Death Star) -- and then seeing their prized super weapon carrying the Emperor evaporate, it's not too much of a stretch that they would lose their nerve and decide to fight another day, especially if the next officer in the chain of command was timid or otherwise not a great leader (conceivable since Darth Vader seemed to choke out the better officers who could think for themselves or had honour).