The reason Wade drafted Mercilus is to keep a fresh rotation of strong pass rushers. That's how the Giants have beaten one of the best QB's in history in two Superbowls. That said, Barwin's value will soar in the offseason, and he won't be a Texan next year. And good for him on his future wealth, which was jeopardized after his ankle injury in 2010.
But for that reason, we're probably taking another OLB in the 1st or 2nd round next year.