His agent got him a 6 year deal on mega wages that no other club is going to come close to matching. I don't think we can expect an agent to bail us out of that decision. If Kalvin wants to take a massive wage cut in order to play a few more years of football in the bottom half of the premier league or in the championship then i expect his agent will be able to find him a club.
At the end of the day, the party that stands to lose the most by him not moving on is us. And everybody knows that. Nobody is going to be bending over backwards to help us out here.