Playing amateur psychologist is a dangerous game with these guys (especially with a guy like Marty, with English being his second language, and his articulation skills probably not being that great), but I almost get the impression he's now becoming much more open-minded about how he's used next season. I think he's probably both seen and read various people's takes on him...he admitted in his bio that he's constantly watching sports programming and reading newspapers, as he feels it's extremely important to stay informed of what's going on around the league at all times...like you say, this man absolutely LOVES the sport of hockey...that comes across loud and clear in his book. And I think some of the open-mindedness is coming from the simple fact that he's beginning to realize that there's not going to be much demand for his services in the off-season, even with his name-brand...Fischler said it perfectly, in that the kind of options available to Marty that involve more playing time will be something along the lines of playing for the Islanders and splitting time with Nabokov. In that kind of a situation, if Marty gets hot, maybe he gets close to 50 games, but if he struggles, it's probably 30, tops, and on a team and in front of a fanbase where he hasn't built up two decades' worth of goodwill. He won't be beloved and embraced anywhere else unless he plays well (as in, MUCH better than the past two seasons)...if he goes elsewhere and he struggles, then he'll just be seen as a washed-up former legend who enjoyed all of his best accomplishments somewhere else. As we've seen, though many Devils fans feel strongly that he should just hang 'em up, that he has absolutely nothing left to achieve, there's a large contingent of pure Marty fanboys who will welcome him back with open arms and won't care if his play declines further next season (sad but true). Overall, he'll get far more of a pass here than anywhere else, especially if he doesn't say one word about playing the following season, what teams he might play for, or how much playing time he's getting.
So though I don't think he should come back, and really REALLY hope he retires, if he insists on playing, I think his one and only option should be to re-sign with the Devils, and fully accept being a 20ish game backup (tops), with the full understanding that he is the #2, not #1A or part of a two-headed #1 monster, and that Cory slumping would not change that, that there's no looking for a crack in the door to kick open if Cory has a few bad games.
I fully admit that not only am I not behind the above, I fear that PDB (though I think his coming back is the right move) can't be trusted with Marty still on the team, and that the potential for this scenario to blow up next season definitely exists. Like I said, I hope it's retirement, end of a phenomenal story.