This question is unclear. If the buyer has delayed the closing date, then different kinds of things need to be adjusted at closing. For example, there are extra days of property taxes now involved. Most lawyers I know would push that cost to the seller because they still had title up until the closing.
The term and financial consequences 'after closing date' is something that has to be resolved between your lawyer and the seller's attorney. As a purchaser, let your legal people tend to this matter, then make decisions accordingly.
The best thing to do is Buyer should talk to their Attorney and Mortgage Broker. They can guide you properly. The Buyer's Attorney may be able to resolve with Seller's Attorney.
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