I don’t know from Grey’s Anatomy (my reaction was, “that show’s still on?”), but I’ve written before about the various types of contracts which exist between writer and reader.
My comment over there at Kristan’s blog covered a few aspects (Sherlock Holmes, Lord of the Rings), but it occurred to me that this applies to a few TV shows that I’ve been attached to over the years.
1) Dallas. Dallas has taken a lot of shit for the “dream season” where they basically retconned an entire season of the show, saying that it had never happened. But they’d broken the contract by killing Bobby Ewing, since the point of the show had been the tension between two brothers, J.R. (evil, charming) and Bobby (younger, earnest, honest). Without that, it wasn’t the same show we’d signed on for.
So, according to what I’ve read, Larry Hagman (who played J.R.) took control, got the new producer fired, brought back the original producer, and went to Patrick Duffy (Bobby) and said, “We need you back.” And so, the contract was restored, by saying that Bobby’s death had been a dream. Not an elegant solution, but the best option available to them at the time. They knew what they had to do.
2) MASH. A lot of people, including me, were upset when Dr. Henry Blake died, but I don’t think that did break any kind of contract. It was more like, “Hey, this is a show about a war. Did you notice that? And you thought nobody was ever going to die?”
3) Dark Shadows never broke the contract, which was, in essence, “no happy endings.” This may be one reason the show has such a devoted fanbase even now.
Barnabas could help other characters become happy, but he couldn’t get there himself. In the final story arc, in parallel time, the Barnabas character (Bramwell) and the Angelique character (Catherine, if I recall) ended up happy and in love, all the curses ended, but we knew that the real Barnabas and Angelique were still going down through the centuries making each other miserable.
At one point, in 1890 I believe, Angelique does something selfless and heroic, and Barnabas realizes that he’s in love with her after all. As he’s about to tell her, she’s shot dead. Her curse on him a century before, after all, included the fact that anybody he loved would die. It was a sad moment, but definitely within the contract.