A lot depends on who we have to replace him. Right now, a Duran/Ref platoon or even a Duran/Arroyo platoon with Kike sliding between CF and 2B looks to project better offense, but I'm not sure Casas deserves to be sent to AAA, right now. As I pointed out, his OBP has been very good over his last 9 games.
I might sit him vs LHPs for awhile, and think about sending him to AAA by mid May, if he's not showing signs of improving, and the replacements are hitting well.
He looked a lot more promising, last fall.
I am far, far, far from "giving up on him," but we need to win, and I don't think sending a rookie down for a week or two should damage his psyche. If it does, maybe he wasn't meant for the bigs, to begin with.