Gallup probably won't be fully back until next year. The usual thing for players coming off that type of injury. Hard to trust your body early on. It will probably effect his route running and his cuts. I doubt if Jones and Co. accounted for this.
At the end of the day, Cooper was the insurance policy. They should not have traded him. We saw this same erosion of the WR corp when Owens and Bryant were sent off. The offense struggled the following season.
How much Prescott can make them all better is the real question.