I just have to believe that this organization, with the coaching staff that they have, and the quality of players they have on defense (Flowers, Hightower, Butler, McCourty, Chung, etc.) will find a way to make the defense at least average. If it's average, that should be good enough, given the caliber of the offense (best in the NFL), to be a legit SB contender again.
Because they've been so bad to start the year, their final rankings may be in, say, the low 20s when all is said and done. But all they need to be is average FROM HERE ON OUT.
I think they can do it. In the TB/BB era, they've been ranked worse than 10th in scoring defense three times going into this year (17th in 2002, 17th in 2005, and 15th in 2011), but worse than 10th in yardage defense 9 times (24th in 2001, 23rd in 2002, 26th in 2005, 11th in 2009, 25th in 2010, 31st in 2011, 25th in 2012, 26th in 2013, and 13th in 2014).
Of those years (re: yardage D), they made the AFCCG 5 of those 9 years and went to the Super Bowl 3 of those times, winning it twice. So clearly having a subpar defense isn't necessarily a game-ender for them.
They just have to find a way to keep the other teams' scoring down some. I think they'll figure it out.