Not many people may be aware that the ending to the 1983 modern comedy classic, National Lampoon's Vacation, is actually a completely re-shot resolution. As in the final version Clark Griswold (Chevy Chase) and his family finally arrive at the Walley World amusement park, only to find it closed for repairs.
However, in the original ending, after purchasing the BB gun, Clark also buys a map of the stars homes and tracks down Roy Walley himself at his house where he is having a meeting in his backyard. Clark gets revenge on Walley and his employees by holding them at gunpoint and forcing them to entertain him and his family by singing and dancing for them. The police show up to arrest Clark and are about to take him to jail when suddenly, the mysterious beautiful woman in the red sports car played by Christie Brinkley shows up and reveals herself to be Roy Walley's daughter! After some coaxing, she convinces her father to drop the charges.
The final scene was to show the Griswolds on a plane heading back home (wearing complementary Walley World hats) only to find out that they're on the wrong flight! Clark then hijacks the plane and attempts to get the pilots to change course.
After the movie wrapped and was edited, it was shown to test audiences, and according to director Harold Ramis, they were highly entertained by the film, however, when the film came to the ending, the audience was less than pleased, mainly because the actual Walley World park was never shown, despite having been built up to for the whole film. So, John Hughes was brought back to write the new ending and Warner Bros. allowed the cast and crew four days to shoot the new footage, which was filmed at the Six Flags amusement park.
None of the footage of the original ending has surfaced to this day, only a few photographs have been released. Chevy Chase announced on the audio commentary for the film's 20th anniversary DVD that he possessed a copy of the film with the original ending, but Warner Bros. has shown no interest in releasing it in any way.
EDIT 1/17/18: In the end credits of National Lampoons Vacation a still of the family on the plane is shown. However, it isn't confirmed that this was an actual still from the ending. But it is most likely.