I have been around long enough to see this tactic play out many times. It seldom generates the desired long term results.
Every player is risking injury every time they step on the field. It's part of the game. That is part of the reason why the average NFL career is about 5 years or so.
In my opinion, Cook is over valuing his worth and is hurting his reputation by his actions.
In most cases, giving a rb a second huge contract is a mistake. I know, you can argue that it worked out for the Eagles and the Ravens, but their success was not mostly driven by their rbs. Those teams are loaded.