That was so much fun I think I'll do some more. Once more, spoilers ahead!
The Phantom Menace
Darth Maul chops off Jake Lloyd's head. George Lucas figures he should cast someone else. Obi-Wan chops off Jar-Jar's head. No replacement necessary.
Attack Of The Clones
Natalie Portman realizes she is running circles around Hayden Christensen's acting and decides she'd rather be with Obi-Wan, who decides to handicap Anakin one episode early, so we can skip all of the bad acting and get straight to Episode III. And BTW, Luke and Leia are really Kenobi's kids, but we don't find that out until many years after Bakura when the whole group appears on Maury for the DNA tests. Obi-Wan waits as a shiny apparition in the green room while the crowd boos him. But, he gets revenge when he disentigrates all of them, including Maury and his hair coloring. Luke and Leia are both relieved not to be related to the over-actor, but Luke is also very confused because he thought he inherited that from his father. "That's your uncle Owen talking," Obi-Wan says and they all have a good laugh! The End
Will Smith can't really read alien script so he pushes buttons at random aboard the alien spacecraft. Oops, that was the self-destruct button-BOOOM! Earth gets a few more weeks of bombing, but eventually the aliens die from viruses just like in War of the Worlds.
Rocky beats Appollo Creed, the theme music blares, he finds Adrian and tells her he loves her.....and he drops dead of a heart attack. The End.
The 80s change forever.