The naming rights are just an asset of the company that bought them. I haven't seen information on the term of the current rights deal, there is a question of whether it was extended, but whatever is left on the deal, including options to extend, will become an asset of NewBank. Usually, the owner of the naming rights can change the name, though they may have to pay for signage changes. There could be some deadline by which they would have to change the name, but in simple terms they still have the rights to call the field whatever name they want. Usually, they will change it to the new name. The naming rights won't be opened for bidding until the current term expires and the current holder of the rights does not exercise any options to extend the deal. In fact, if the NewBank wanted out of the deal, they would probably have to pay some early termination fee.
Just look at the Wells Fargo Center in Philly. Through a series of bank mergers, that venue's name changed from CoreStates, to First Union Center, to Wachovia Center, to Wells Fargo Center.