Sean Lee has the potential and talent to be the best DEFENSIVE player in the NFL in my opinion, not just the best middle linebacker. He works very hard, is extremely athletic, and has proven that when he's on the field he's a true game changer for the Cowboys defense. I would sign him to a long term deal just based on his potential alone, he is worth taking that risk. But like someone said, I'd like to see them be a little conservative with the guarantees given his injury history.
I really think when the Cowboys went out and signed Monte Kiffen, they really invisioned transitioning from DeMarcus Ware/Anthony Spencer to Sean Lee/Bruce Carter as the focal point of their defense! In my mind is not a bad move at all given Ware's age. If Lee/Carter are healthy, this defense has the potential to be dynamic and one of if not the best in the NFL, but it's a huge gamble. If it fails everyone's going to play Monday Morning QB and criticize the hell out of them, but you need to take risks to get where you want to be and I think this is a good bet to make!