While Banta-Cain is listed on the roster as a 3-4 outside linebacker, I view him as more of a rush end when the team plays a four-man line or is in sub packages in passing situations. He's at his best when getting up the field and not being asked to set a hard edge in the running game.
Six-year veteran Rob Ninkovich and 2010 second-round pick Jermaine Cunningham currently project as the top 3-4 outside linebackers, playing on early downs. In 2010, they would often come off the field on third down in place of Banta-Cain.
So if the Patriots were looking to veteran free agency to fill the void and provide themselves some insurance, they don't necessarily have to lock in on a pure 3-4 'backer. A 4-3 edge rusher could also fit.
Veteran Eric Moore, a late-season signing from 2010, likely steps up to replace Banta-Cain. Marques Murrell, who played in the team's 2010 opener before being cut and brought back late in the year, is back in the mix along with 2011 sixth-round pick Markell Carter of Central Arkansas.