Sharon, since you are not supposed to earn money from a short sale transaction (it usually states this in the short sale approval) .. . The bank is the one that should be owed the deposit, however, keeping a buyer's earnest deposit can be tricky....they must agree to cancel escrow and forfeit their deposit... If they will not sign this cancelation then you can run into problems.... It may be best to move on to a new buyer if the bank is not asking for their money... so far I have not had a bank request the buyers deposit...but it could happen....
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!