Grey's Anatomy fans remember where they were when McDreamy died. It was one of the most shocking moments in the show's long history, and one that would be referenced countless times afterwards.
Derek Shepherd (Patrick Dempsey) was one of the most important characters on the show when he was killed off, and as such, the writers and producers spent a lot of time figuring how to best handle the storyline. Interestingly enough, the writers worked up three possible outcomes for the character, before settling on the one they ultimately chose.
Grey's Anatomy writers considered keeping McDreamy alive
This revelation came about during a Vanity Fair interview with executive producer James D. Parriott. He noted that there were actually two outcomes in which Derek Shepherd was kept alive, and simply maintained his relationship the titular character, Meredith Grey (Ellen Pompeo), offscreen.
The first would have relocated Shepherd to Washington, D.C. and the second would have had Shepherd survive the car accident that eventually claimed his life, and simply have the romance between him and Grey gradually weaken. The decision was ultimately made to kill the character because it was deemed the simplest.
Parriott said the other outcomes would have led to too many narrative complications:
""[We] decided that just bringing him back was going to be too hard on the other actors. The studio just said it was going to be more trouble than it was worth and decided to move on.""
Part of the reason Dempsey was excised from the show was that he was getting into increasingly hostile exchanges with creator Shonda Rhimes and the rest of the cast. It reached a point, according to producer Jeannine Renshaw, where Rhimes gave ABC an ultimatum: either Dempsey goes or she goes.
Patrick Dempsey and the Grey's creator had tension on set
"Nobody wanted him to leave, because he was the show," Renshaw added. "Him and Ellen. Patrick is a sweetheart. It messes you up, this business." The network ultimately sided with Rhimes, however, and Dempsey was ceremoniously written off.
Ultimately, the showrunners and producers are happy with the decision they made. They felt that it would have been inaccurate to the character of Derek Shepherd if he had left Grey and their children behind, and that death was the only concievable reason he would no longer be around.
Stacy McKee, another executive producer, said as much to Vanity Fair:
""I don’t think there was any way to exit him without him dying. He and Meredith were such an incredibly bonded couple at that point. It would be completely out of character if he left his kids.""
It's hard to argue with that reasoning.