If one party is not ready to settle on the due date, the other party can issue a notice to complete. The notice to complete provides the defaulting party 14 days from the issue of the notice to settle the transaction. The party who is not in default can then terminate the contract and the deposit will be paid to that party. This sometimes means that the buyer will forfeit the deposit if they are unable to complete the settlement by the end of this Notice period.
Note that the seller is often in a unique position where they can also charge interest for any delay caused by the buyer so the consequences for a delay caused by the buyer are significant.