If the Jets really wanted to gut their roster, they could trade Nick Mangold for Draft picks. That would be burning the entire thing to the ground. There really does not seem to be much wisdom in that. Rebuilding is easier if you have some kind of foundation to build around. You do not eliminate all talent when you are rebuilding. You find the pieces you have worth keeping and rebuild around them. It is difficult to say what the market would be for a top center, but it is entirely possible the haul the Jets would receive would be less valuable. One would have to imagine the Jets feel the same way.
It is a good thing that Mangold is probably going to remain a Jet because of how good he is in the middle. Even in what amounted to something of a down year for him, Nick was still one of the best centers in the league. He is a capable pass blocker and a top level run blocker. Anybody who has read this site knows I am a big believer that an offensive line is only as good as its weakest link. It only takes one blown assignment to destroy a play. That's why it is great to have top talent like Nick in the middle of the line. It is a great thing to have confidence that your center is capable of matching up with any nose tackle in the league. The nose tackle's main job is to occupy two blockers so they cannot block others, freeing the rest of the defense up to make a play. When he is on, Mangold wins his assignments to free up the rest of the line to block others.
I think any argument made for Mangold to not return is on very shaky ground. He will be back. The question is what his cap number will be. Depending on what the Jets want to do with his salary, they can potentially clear up anywhere from $2 million to $7 million in space. That money will not disappear. It would go to future years, but unlike the Mark Sanchez extension, such a move would provide minimal risk since Mangold figures to be around a long time.