Unless IPA developed TBP with the explicit and publicly known idea that his work was not to be used in any end-user modifications, I agree with the statement that he has no right to withdraw permission now that TBP is done.
If, either before joining or during development, he publicly stated that his work was not to be used, then in addition to not knowing why the heck he joined the team, it would be perfectly reasonable to not use his work, but in his waiting until TBP was finished, he has forfeited that right.
If he had done it before, then the rest of the TBP team would have the time and ability to find someone to replace him, someone that wouldn't mind having his/her work used by the end-user, but now he's robbed the TBP of a completed project, something I would think is pretty disrespectful in itself, especially when he is the project leader.