That depends on the team's expectations. If the Patriots expectations are an 11-5 regular season with a one and done for the playoffs, then Logan Mankins is expendable. According to Pro Football Weekly, the sacks allowed by Matt Light increased from 2 to 10 from the 2009 to 2010 NFL Season.
ProFootballWeekly.com - Matt Light
How much of the sack increase was due to Dan Connolly playing left guard in Logan Mankins absence or the deterioration of Matt Light's play is subject for debate. However, without Matt Light and Logan Mankins on the left side of the offensive line, the 2011 NFL Draft priorities for the New England Patriots significantly change. Furthermore, the right offensive guard position needs to be upgraded immediately via the 2011 NFL Draft, as well.