First you have probably made a gread deal. I hope every thing closes smoothly as it often does, but have patiene.
Did you sign a Short sale addendum, There you will see that there must be seperate acceptance in writting bt leinholder by a certain date. The form says "evidence of the leinholder's approval and agreement as required (refers to above paragraph) or on terms other wise acceptable to buyer by____date.",and then you may give notice of temination if not.
It also goes on to later state that your money will be refunded , I will again quote " the leinholder withdraws its approval and agreement prior to closing and funding."
What is being said here is The lender must give more than verbal approval and that even then the lender may withdraw its approval. This is why I always advise anyone on this site to use a Realtor that is has done more than one or two Short Sales.
Now I will again say that most Short sales do close but not always in a timely manner, you can not hold these lenders to the same schedual as you would a normal seller, ir you try they will tell you and you agent where what and when to go.
Cangrads and Good Luck