What major question is never answered in "The Cask of Amontillado"? (Look back to the beginning the story)
One major question that is never answered is whether or not Montrestor considers himself to have successfully exacted revenge on his nemesis, Fortunato. He claims that revenge is incomplete unless it can be accomplished in a way that does not result in punishment for the avenger. "A wrong is unredressed," he says, "when retribution overtakes its redresser." He feels that it is not true revenge if the avenger is caught or otherwise punished because then it's like he has been wronged twice by the one who he seeks to punish.
By the end of the story, Montresor's success is somewhat ambiguous. If he feels guilty for the murder of Fortunato and has been allowing it to weigh on his conscience for the past fifty years (he says it has been "half a century" since the events in the story took place), then he has not achieved real revenge because he has been punished by his own guilty conscience. If, however, he has not really been feeling guilty for the murder, then he has achieved revenge because no punishment has been inflicted upon him. Whether or not Montresor feels guilty about his action is uncertain, and so whether or not he's truly been successful in achieving his revenge is likewise unclear.