The Roosters are calling the NRL's bluff on this. Boyd retiring may have saved the NRL a potential law suit far in excess of the value of his remaining contract, so I doubt they will object because he may have done them a favour by retiring early.
Actually, I can see the NRL saying that concussions need to be treated differently to other injuries forcing retirement given how little is still known about their effect on the brain. They will not want to discourage players from making the smart decision to retire early. And maybe there is some merit to that policy argument.