I don't know this for an absolute fact, but I'm pretty sure player contracts cannot just be terminated by a team based solely on a "whim". Pretty sure they'd have to show cause in order to make it stick. Sounds like simple contract law to me.An NFL team can terminate any players contract on a whim, with no ramifications.
I mean, a team could attempt to do it, but I'm pretty sure the CBA would not allow it without ramifications. By the same token, players cannot simply terminate a contract.