I think this really comes down to O'Brien. If he ends up with the Texans, then he'd badly need a QB, and may not want to use the #1 overall pick on one. The Texans have been awful on the edges this season (3 sacks for Brooks Reed, 7 for Mercilus although 5 were either unblocked or against backups), and they could use a guy like Clowney (or whichever other pass rusher they prefer) as long as it doesn't also prevent them from getting their QB.
My best guess is that if O'Brien goes to the Texans, then Mallett is traded there for the 33rd overall pick next offseason and a conditional 2015 pick, starting at a 4th if he's not the primary starter and maxing out at a first rounder if he takes the Texans to the playoffs. If O'Brien thinks that Mallett is a legitimate NFL starter, then he's easily worth the 33rd overall pick and like a 2015 4th to try out. If he takes the team to the playoffs in his first year as their starter, then he's easily worth the 2014 33rd overall pick and 2015 22nd overall pick or whatever it'd be.
The primary alternative for O'Brien with the Texans would be drafting a QB 1st overall, and while a rookie and Mallett are similarly unknown to most coaches around the NFL, O'Brien would have a much better understanding of Mallett's value than he would of a rookie.
If O'Brien doesn't become an NFL HC or does but goes a different direction at QB, then yeah, they're probably holding onto him and taking the 2016 6th round compensation pick after he signs with the Browns in 2015. If O'Brien is a head coach and wants Mallett, then the Pats have leverage because they know O'Brien sees Mallett as a starter. If not, then there's really nobody else in the NFL with any inside knowledge of Mallett, outside of a surprise McDaniels hire.
