1) Lost
One of the most famous abandoned story arcs that would have completely altered its show is the original idea for the pilot of Lost. Perhaps inspired by Alfred Hitchcock’s Psycho, main character Jack Shephard was to be shockingly killed by the smoke monster within the first episode. Evangeline Lilly’s Kate would then have become the leader of the survivors.
At that stage, former Batman actor Michael Keaton was set to star in the role, in a clever piece of stunt casting that would further convince people that Jack would be sticking around. Studio execs disliked the idea, however, feeling that audiences would feel cheated.
As such, Jack was revised and promoted to series regular. Because of this, Keaton backed out of the part, not wanting to commit for the long haul. Instead, Matthew Fox claimed the role, after originally auditioning for Sawyer.
It’s fair to say that if the original plan had gone ahead, Lost would have been an entirely different show.