If Marty comes back next season, he's going to take a reduced role imho. If that's not good for him, which I don't see being a problem, he's going to retire. This is all assuming he finishes this season healthy and in good standing. He's talked about maybe paying elsewhere and all that, but lets be real, the chances of seeing him in another sweater are basically zero. Lou is not going to push him out the door, but both men know that next year is way too important for the future of the franchise. If they plan on having Cory stick around, he's got to be the man next year. They have to make the transition.
Marty is still plenty capable, but the consistency is just not what it used to be. He can't maintain his highest level for as many consecutive games as he used to. It used to be that he would get into a zone and it would / could last for months. Now, if you get two or three solid games, it's best to spot the guy and give him a break. And this is just going to degrade as time passes by. This is a transitional year for both him and Cory and it should be that way unless Marty completely falters. You just don't dismiss the perosn who has been defending the goal for 2/3 rds of your franchise's existence. Next year, however, the timing is optimal to pass the torch and for Marty, if he wants and is capable of hanging around, to become a backup.