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I'm sorry to hear about your situation. Worst case scenario is that the buyer sues for breach of contract, you pay the attorney fees, costs, interest, AND "specific performance" (meaning that you transfer the property to the buyer). Specific performance is the type of damage that you can expect being the seller of real estate, as all real estate is unique. You can't really pay the monetary damage when you had a contract to sell the property.
Now as to what's the most likely scenario, that's hard to tell, and ultimately depends upon the buyer. If the buyer is dead set on the house, he can force the sale of the house. But if the buyer is willing to back out, then there might be a better option available to you (settling with the buyer for a lesser price, where you get to keep the house).
Hope that clears things up a bit. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable.
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Thank you, ***** ***** luck to you!