From a legal stand point i believe we are still entitled to commission on that sale, however we have not called upon the vendor to pay these fee's and would prefer to just resell the property and not charge them twice.
It's happened to me once, where my purchaser was unable to obtain finance in time. We rescinded the contract, and took his deposit (which was only $500 and well short of our extra holding costs anyway), and then accepted another offer from the same buyer a week or two later, when he had his finance approved. The agent didn't charge us double commission, though legally, he could have.
A guy that I know had a parcel of land that he bought for $1M. He got a DA on it which increased the value to $7M.
He took the loan up to about $4M to put some cash into another development. He then had a buyer who purchased for $7M, subject to the vendor withdrawing his own DA, so that the buyer could lodge a different DA (you can only have one at a time, at least in this area).
In the days before settlement, the buyer got the impression that his own DA wasn't going to be approved, so he just refused to settle. Even with a $100K deposit - which he forfeited - the vendor lost out
big time. He now had a property with no DA, whose value had dropped back to around $1M. And the rules had changed such that the DA which he previously had, could no longer be obtained.
And of course the purchaser was structured in such a way that there was no hope of retrieving any damages from them for the breach.