Classic risk vs. reward scenario. The risk is high for the Pats now because of Brady's knee. The value for Cassel now is probably as high as it is going to get. Assuming Cassel gets traded before any preseason games are played, there is precious little chance for him to improve his stock...and a whole mess of situations where his stock can nosedive:
a) Market dries up due to free agency, draft, teams getting comfortable with what they have in-house, etc.
b) Cassel gets hurt in mini-camp or falling off the solid gold toilet he can now afford.
c) Teams spend money on other needs and can't afford a big contract for Cassel.