Pratt is going to be signed to the practice squad if he clears waivers. It's unlikely another team will add him to their 53-man roster, so chances are he will return to Detroit.
Mixon is also a candidate for the practice squad. Signed as an undrafted free agent after the NFL lockout ended, Mixon had a solid training camp. He wasn't good enough to unseat any of the linebackers from their spot on the roster, but he could return to the practice squad.
Chambers was brought in as tackle depth when the Lions were dealing with injuries at the position. With Jeff Backus, Gosder Cherilus and Corey Hilliard all healthy now, there was no real reason to keep Chambers around.