He's free to do what he wants.
However, I think his ego led him to make a poor decision. Even if you're a backup, you remain a valuable contributor to the team. Besides, when it comes to lines, is there really such a thing as backups when you've got all sorts of rotations and the likelihood of injuries?
You don't take your ball and go home at the first moment you disagree with management. I don't like when anybody does that. Makes you look small.