IMO, Cassel served his purpose. The Bills had, at worst, three low level starters/high level backups. After re-signing him, Cassel was expendable because he was never going to be the starter. Whaley knew that there would be desperate teams, like there are every year, that would want to trade for one of his backups. If they could get a 2nd or 3rd for EJ, he'd probably have been gone. If they couldn't, they would just trade Cassel. Signing Cassel back was basically a freeroll.