Looney Tunes - The Heckling Hare Lost Ending (1941)

The Heckling Hare is a 1941 Bugs Bunny theatrical cartoon that featured Bugs chased by a dog named Willoughby. As its final gag, the legendary Tex Avery had Bugs and the dog fall off a cliff, avoiding their doom by suddenly putting on 'air brakes' right before they hit.

Cut Ending
However, the plan was for this gag to be repeated twice more, with Bugs and Willoughby's final fate left hanging. Either because of a risque line, the fear of audiences thinking Bugs had died, or the sheer length of the fall sequence, Leon Schlesinger had the cartoon edited to just one fall with an abrupt cut (that is sometimes further edited in syndication). This infuriated Avery, who promptly left to begin his historic run at MGM.

Fate of the footage
No mention of the footage (which might have proven valuable for recycled use in other cartoons later on) being destroyed was ever made, but nor were any preservation efforts ever described. The fate of film footage in that era, while better than prior ones, was still not at all a certain one. Fans of classic WB animation continue to search archives and collections for the possibility of finding this and other lost Bugs footage.