Without knowing the exact communication between you and your attorney, it cannot be determined whether the attorney failed to do what they were hired to do. As stated by @Steve L.f you asked them to draft a release and they drafted a release, they did right by you and you should pay for the work. The question is whether you told the attorney the story and explained what you wanted to happen (i.e. get a new contract).
That being said, I do not believe what you wanted was legally achievable. I am not intimately familiar with TOPA, but from my brief reading on the subject, it appears that any time an owner wants to sell, the owner is required to notify the tenants. So, TOPA was violated already because the owner entered into a contract with you and did not notify the tenants. The only way around the situation (from what I can see) is to have delivered the proper notice to the tenants and waited the time for them to decide -- if they were agreeing to move out, most likely they would not have jumped through the hoops to purchase and you would postpone closing approx. 2 months. I do not see how releasing the contract would change that at all. If you entered into an agreement saying that the owner would agree to a sale contract after the tenants moved out, I think TOPA would still be triggered -- agreeing to agree to sell would probably be considered the same as agreeing to sell.