Good luck passing the pub test if the NRL refuse to allow medical retirement on the basis of a head injury.
To me TMM has recovered from his previous injury and been given clearance by the doctor to return... I would suggest his slate has been wiped clean and therefore a reoccurrence should be treated as a new injury.
That may not be how their wording allows it to happen, but if they refused it there would be significant negative backlash from the community (not just league, but outside the sport itself)... it would likely cause significant reputational damage.
It would be like a guy retiring due to cancer, making a return after it's gone into remission from treatment, but the NRL refusing to allow medical retirement if it comes back... the shit storm rained down on NSWRL HQ would be massive.