Judging by the condition of the player in question when he arrived at WTW last season, I'm not convinced that his professional reputation is at the forefront of his mind.
However, I sincerely hope that all the SL Chairmen who received this letter replied with an unequivocal no, and that the RFL do the same - someone at the club has cocked up and I can see no justifiable reason that they should be allowed special dispensation to compensate for that cock-up. If they are, several clubs (including Cas) could feel justifiably aggrieved that they weren't afforded the same opportunity.
As has been pointed out, the club will have to honour the value of his contract and I guess he'll become a free agent; in short, tough titties.