Contract questions are best answered by attorneys. In general, As long as both Buyer and Seller still want to complete the sale, the simply extend the closing. Keep in mind that either party may incur extra costs due to the delay, including taxes, insurance, loan fees (which should be waived if your lender caused the delay), etc. The extension amendment can include an adjustment for those items. Be careful NOT to change anything that affects the loan underwriting, or a longer delay can result.
Doc Stephens, REALTOR