Cities and Local Government Devolution Bill [HL]

If, for example, my own area of Sheffield decides to go for this with a mayor and it is then not deemed to be as successful as some of the proponents want and the public and the politicians in that area wish to move away from the mayoral model, what would be the procedure to do that—to prove that it was not an imposition, that actually it was a deal, it was voluntary and could be withdrawn from by both the public and the politicians of that area?