Lucus has shown that the overall story has been pretty fluid, like Leia being Luke's sister. In several drafts of TESB, Vadar was not Luke's father. Annakin Skywalker would appear and help Luke confront Darth in one story idea. Kenobi was suppossed to train Luke right until the end. His death in SW was a last minute idea.
Also, the trilogy or nine-part was always going to end with the destruction of the Death Star (withthe Emperor aboard) When Lucus was cutting his script down for ANH, he realised that by moving a lot of the plot to later films, he didn't have an ending for ANH. So he stole the DS ending. When he got to Jedi, he was buggered. So he took the interesting move of repeating himself, with a bigger Death Star.
------------------ 'His limbs flail about as if independent from his body!' -Chandler Bing on Michael Flatley.
He wont let them. NO-ONE is allowed to touch the franchise after he's gone. And if they do, he'll come back with a blue aura, and reverb on his voice, and, erm, shout at them to stop or something.
------------------ 'There's no meat in beer, right?' -Joey Tribiani