About this work
What happens on the day the deal does not close?
Nothing formal, which is part of why it goes badly. There is no filing, no hearing and no official notice. There is a closing date in the agreement, it passes, and the party who could not perform is in breach of contract from that moment.
In practice the lawyers exchange letters. One side tenders, or records that it was ready, willing and able to close and the other was not. The other asks for an extension. Whether an extension is granted is entirely a matter of agreement, and the price of one is usually a further deposit and a contribution to the costs the delay has caused.
The single most useful thing to do in the first 48 hours is preserve the record: what was sent, when, what the lender said and when it said it, and what each side was actually able to do on the day. A failed closing is litigated on whether each party was ready, willing and able to perform, and that is proved from contemporaneous documents rather than from recollection eighteen months later.
The second most useful thing is to stop the loss growing. A seller who does nothing for four months while the market falls has a larger claim on paper and a harder one to prove, for reasons the duty to mitigate makes obvious.