If Dark Shadows had been canceled in mid-to-late 1968, everybody would have said that the Adam storyline killed it. But it wasn't canceled. Instead, it proceeded on to the the Quentin's-ghost storyline and to 1897, considered by many to be the show's finest hour. Gothick has said many times that Dan Curtis pulled the plug on Dark Shadows. If that isn't correct, I still figure that when Curtis heard that ABC was planning to cancel, he could, if he wished, have pulled a rabbit out of a hat to save the show. But after five years, Dark Shadows was been-there-done-that-wore-out-the-T-shirt for him, so it died. (And then, as was only appropriate, it refused to stay dead.)