While that is not a bad assumption, he has yet to say he is done pitching. While I think he had plans of hanging it up after this season, he left the door open for a reason like this. An injury like this may have been one of the few reasons he did not announce he was retiring at season's end, instead choosing to say words to suggest he is retiring without saying it. If Rivera returns in 2013, he is not "un-retiring" like fellow Yankees pitchers such as Andy Pettitte and Roger Clemens. Because he never officially said he was retiring.
Nobody wants to go out like this. It is fair for Mariano to have concern over his return since he has not been operated on yet. He has yet to undergo any type of rehabilitation, nor physical therapy on his knee. He does not know 1) how the procedure will go and whether it will be successful, 2) exactly how long it will take before he gets to rehab his knee, 3) when he will be able to throw again and 4) how long it will take before he can return to game action. He is not crazy for having doubts at this stage of the game. A lot has to happen before he can even think about returning. To me, its not evidence he is close to retiring.
And knowing what kind of competitor Rivera is, there is no doubt the fire exists to get back into game action. To be in the shape he is, at his age, takes a lot of hard work and determination. Would it be insane if he managed to make a return this season before the playoffs? It certainly would not surprise me. And if he doesn't, it will not be for a lack of trying. It is very feasible that if Rivera is not ready at the end of the season, he will just miss it by a little bit of time. Meaning he will just about be in game shape when the season ends. In my opinion, it makes no sense to hustle to get back into action without actually doing it. The only instance where that makes sense is if there is a major setback, which are more common in elbow and shoulder injuries than knee injuries.
I think if Mariano Rivera returns this season, he will retire when it ends. If he gets one more chance at the postseason, he will retire. Like I said before, if he doesn't return this season, it will not be for a lack of effort. I predict he will be very close to returning before the season ends. If he just misses out on returning, he will come back next season for one more. If not, he would have said "I am retiring after this season". He did not say that just in case something like this happened. We have not seen the last of the greatest closer in the history of Major League Baseball pitch in his last game. He will be jogging in from the bullpen to Enter Sandman either at the end of this year or next year.