Was there an inspection period or was there a due diligence period in the contract? Pretty much the bottom line is "How much do you want to sell the house"? Dates and deadlines are more of a goal than a cast in stone date unless certain terms and legal language is used. The buyers can always walk away, the question is what will the consequences be if they do. You might get their earnest money, but you won't be selling the house to them, so is that you goal now?
Just to add; you are obviously working without a Realtor, or you would not have to ask these questions.
If the Buyer also is working without a Realtor, and did not include the normal Contingencies; then you both will end up with what you create; confusion!