Croshaw will be able to go anywhere. I'm sure he can negotiate his team to sign with him. This was either very bad move from them or it's what they planned for some reason we don't know about.
It's very frustrating thinking of how great this game could have been. It was barely a game at release and hardly anything has been added to it. I haven't been following for a few years but I wouldn't be surprised if Niantic removed all pokemon and just added a "give us money for no reason" button.