I want to start off by saying that Mario Williams is one of the best defensive players in the league. He actually was a top-10 defensive player in the league before Wade Phillips, the defensive coordinator for the Houston Texans, moved him to outside linebacker to fit in the 3-4 defensive scheme that he implemented.
Williams' contract is set to expire this offseason, and it wouldn't be a wise decision for the Texans to bring him back.
Despite his season-ending surgery that he sustained earlier in the year, the Texans didn't really have a drop-off in pass-rushing production.
They compiled 30 sacks in 2010 but then finished the season with 44 this year. The emergence of J.J. Watt and Brooks Reid certainly played a factor in the 14-sack improvement from last year, and they have both made Williams expendable.
Secondly, "Super Mario" is prone to injury. He missed the majority of the 2011 season with a torn pectoral muscle (ouch).
Another thing for the Texans to worry about is where they are going to get the funds to finance a Pro Bowl-type of contract that Williams deserves. Most of their money is going to be focused towards re-signing Arian Foster.
The Texans have other needs besides a pass-rusher, so they should let Williams walk and get paid somewhere else.