I have had this happen with one of my transactions and in that instance, all contingencies had been met and the buyers were not coming to the closing table, and all notifications have been sent to the buyers that we were going ahead with the closing, they had to appear or be in default of the deal. Once in default, procedures were initiated to retain the down payment money and the end result was that the contract was cancelled and monies retained.
Please open a line of communication with your attorney to get a full understanding of what is happening in your particular situation and what your options are.
I am very sorry to hear about your situation and frustration, I Wish You Good luck...
This is a legal question, please contact your atty and find out what's holding the closing on buyer end, the reason for the delay and what are your rights.
Also you can check your contract to see if the buyer still have enough time for the closing (date) or it's already passed a while ago.
This probably a better question for a the attorney that drafter your contract.
You might also research the concept of "specific performance".
My experience is that it is rarely applied as a remedy, but I am not an attorney and they would have better answers for you. Good Luck!