cousins didn't play well enough to cause a QB controversy (i.e. force a trade), might as well hang on to him for a year unless you get a great offer
Honestly, I don't see any point in keeping Cousins except for the salary cap value. He may be cheaper than bringing in a veteran/journeyman backup.
But this team is in such a need of talent, particularly in the trenches, that it's hard to justify holding on to Cousins and not taking a third rounder or better. Just simply too many holes that, if not filled, will result in Cousins playing too much.