I get that opinion but someone in his shoes could also elect to stay for less. The Dolphins have paid him over 85 million dollars and like you said ... he really only has a little time left. I'm not sure that making a few more million is going to change his life. at this point. Dan Marino chose to retire rather than play for the Steelers and who knows else. It's a different decision for each player and I can respect that.
I don't think you can really bring Dan into the conversation - by the time he retired he had been with us for 17 years. He never had great knees to begin with, and at the end he was completely gassed both physically and mentally. He also got paid plenty every single year he was with us. While the Vikings offered a King's ransom for him to go on another year, it was always going to be unlikely.
X has played 8 years for us (admittedly in a more physical role) and in the right team may still have have a couple left as an effective contributor, and may even get a championship ring. As it looks right now, that team won't be the Dolphins. He's done plenty for us, and I don't begrudge him making a move and continuing his career.
I think what's more telling is the line of other players who have bolted out the door since X was told he was not in our future plans. Wilkins, Baker, AVG, Davis, Jones, etc. Almost all of these guys have only been in our team 4-6 years, and left at what should be approaching the prime of their careers. That stings a hell of a lot more.
Even with X leaving (and some contract restructures), the huge contracts handed out to Armstead, Chubb, Ramsey and Hill are biting us hard. Williams wants huge money to stay (he probably won't), and we haven't even started talking about the Tua situation (who up until now has given us a lot of cap relief).
Last season was a boom or bust proposition once we splashed out on Ramsey and then Chubb - that's left us zero space to move now. The rebuild is looking more and more like a failure the longer it pans out.