What stories could you tell from memory? What stories would you want to tell at the end of the world? For the characters in Mr. Burns: A Post-Electric Play, staged this weekend at Middlebury College, the answer to both questions is “Cape Feare,” a 1993 episode of “The Simpsons” in which Sideshow Bob makes one of his many attempts on Bart Simpson’s life. The play, directed by Alex Draper, follows this story as it is recalled by a crew of apocalypse survivors, as it morphs several years later into a traveling stage play, and as it transforms over decades into folktale and legend.