He was fading fast before the injury.
Against the Rams, they targeted him a whopping 14 times--he caught 6 balls. After the they were essentially done with him as a pass catcher.
Bringing him back would certainly satisfy Beane's kink for washed up WRs on their way out of the league, but I think even he doesn't have a 1 year contract with Cooper's name on it in his pile.