Tom's wife certainly does get more than she bargained for when she goes into the forest to do business with Old Scratch. All that Tom finds left of her is her heart and liver tied up in her apron, hanging from a tree with a vulture hovering over it. Her gruesome fate contributes to the story in several ways.
First, "The Devil and Tom Walker" is an example of Romanticism in literature. Mystery, death, and strangeness are all elements of Romantic literature. Tom's wife's dying in such a strange and mysterious way contributes to the story's strong Romantic tone.
The horrible nature of her death also contributes to the theme of the story and to Tom's character development. She is a very, very greedy woman; she is so greedy she will deal with the Devil himself if it will enrich her. For her to die in such a shocking way emphasizes the terrible results of greed. Also, Tom's reaction when he finds what's left of his wife's body shows a great deal about him. He is only upset because he has lost his property. Finding her heart and liver doesn't seem to faze him, but he does notice the signs of a fierce battle. He assumes she put up quite a fight:
Tom knew his wife's prowess by experience. He shrugged his shoulders, as he looked at the signs of a fierce clapperclawing. "Egad," said he to himself. "Old Scratch must have had a tough time of it!"
Tom clearly did not love his wife! In fact, he was glad she was dead:
Tom consoled himself for the loss of his property with the loss of his wife . . . .
Tom is so hard and cold emotionally that even the horrible way his wife dies does not move him at all. Like her, all he loves is money.