The declining action takes place after the Devil whisks Tom away. At this point, the climax has been reached (The devil taking ownership of Tom Walker's soul). Some elements of the denouement could be when the town people return back to Tom's home to find his riches reduced to virtual nothingness and his home burning to the ground. The withering and devaluing of all of his assets could be an example of how the declining action fits the climax. I think you could make a case for other moments being representative of the climax, but in terms of a strict structural element to the short story, the climax would have to be when the Devil comes to his home to claim Tom. Therefore, what follows would represent the falling action leading to story's resolution.