All this talk about "we also got his services for a decade" (or whatever) is disingenuous malarkey, nothing more than the stuff of homers. Yeah, they got his services while he was contracted to the team. No kidding. That's how pro sports works, that's how legally binding contracts work. But if he leaves via free agency, the team gets nothing -- absolutely nothing -- from it. That is the discussion, not this stuff about the last 10 years. The last 10 years provide no benefit to anyone moving forward. The only thing that comes close to the relevance of the here and now is the (now theoretical) trade-off between trading him recently before he had the chance to go to FA, and thereby recouping some assets, versus keeping him as basically an own rental. The rest is ancient history, nostalgia, irrelevance, none of which help restock a roster. Nor does it allow a team to go back in time for a re-do, which actually would add value to a player's past career. It's like buying a new car and instead of trading your old one in for a few bucks off the price, you just give it to the dealer because "I got its service for the last 10 years so I don't care about any value I can generate out of it now." If that's your business philosophy, you deserve to be suckered in every deal.
You mention the Jets get his cap space back if he goes FA. Yes, that has value; thank you for that dose of reality. But the nostalgia? Sorry, that's completely worthless to asset management (except to set an upcoming AAV, or the cost of a trade in those cases).