Is the short sale approved or not? Where are you with the bank?( my guess, the price and terms are already approved, am i right?)
You probably still have time to cancel your agreement with these buyers ( since they are not able to proceed) and accept another offer, send it to the bank, close and collect your relocation fee.
Have your realtor ask your escrow officer what to do... Or on a brighter note, is the investor/buyer almost ready? Perhaps the bank will give another extension...sometimes they will do this especially if the buyer is willing to pay a per dium fee for their tardyness....(money for each day they are late closing usually about $100 a day)... Make sure that if you go this route that the buyer is ready to perform and that he/she understands the timeline.
Also, if this does not work out and you move on to another buyer make sure your agent checks the buyers bank statements for funds to close and/or approval letter from a direct lender... In a short sale a buyer must be educated on the process. Make sure your agent lets the buyer agent know how the process works and that they and their buyer understand completely. Comunication is key to a succesful short sale. good luck!