In "The Cask of Amontillado," what would have happened if Fortunato, for any reason, had declined to accompany Montresor to his palazzo that fatal night?
Montresor's gambit is contained in these words: "But I have received a pipe of what passes for Amontillado, and I have my doubts... You were not to be found, and I was fearful of losing a bargain... I perceive you have an engagement. Luchesi--"
It is part of the criminal genius of Montressor that he knows how precisely to hook his intended victim and then slowly reel him in. Of course, the question points out the way in which Montressor's plan depends on Fortunato acquiescing to Montresor's proposal to test the quality of the wine. Yet this temptation has been carefully planned by Montressor and he shows a disturbing understanding of how Fortunato's mind works, both in the way he recognises Fortunato "prided himself on his connoisseurship in wine" and also the jealousy he will feel if Montressor is forced to go to Luchesi to seek his opinion. It is the combination of these two factors that makes Montressor's request so impossible for Fortunato to refuse. Note how Montressor repeatedly gives the appearance of doing everything he can to put Fortunato off, whilst of course doing this in such a way as to only increase Fortunato's desire to go:
My friend, no; I will not impose upon your good nature. I perceive you have an engagement. Luchesi...
All it takes is the reference once again to Luchesi, whom Montresor has already compared to Fortunato in terms of his knowledge of wine, and Fortunato is determined to prove his superior knowledge by tasting the amontillado for Montressor.
This question is therefore completely right in the way that it indicates Montressor is risking everything on this plan to tempt Fortunato into his catacombs, and if Fortunato refused it would be very difficult for Montressor to explain himself the next day. However, part of the story is the way that Poe, through the use of the first person narrator, reveals just how carefully Montressor has studied Fortunato's character so that he is able to manipulate him just as he wants. Montressor shows an excellent understanding of Fortunato's psychology which he uses to ensure his success.