Is there a law as to say how many times a home closing can be rescheduled before the seller could legally back out. If none of the reschedules are the sellers fault?

There's not a law but there is a way to handle it. If the buyer is constantly postponing the closing and you have gone past the estimated closing date listed in the contract, then you can send a letter to the buyer scheduling a new closing date for 10-14 days away, for which "TIME IS MADE OF THE ESSENCE OF THE CONTRACT". If the buyer fails to close by that date then they will be considered to have defaulted and the seller can declare the contract terminated. At that point, depending on what the contract says, the seller should be able to keep the deposit money and re-list the house for sale.

If you are currently in this situation then you really should speak to a real estate attorney asap.