I personally am not as concerned about the corners and safeties as many others are. Also, something to note is that Torrence was a WR convert and has only been playing steady CB for one full season and change. Not making excuses for his deficiencies, but considering the fact that he's still growing into the position and moved there because of depth and talent issues last year...he's not so bad. I actually think he played decent there last year. Not great, but for a first year starter at the position, not too rough.
On top of that, with Chekwa and Hines, we have two potential 1st team All Big-Ten performers. Chim could be a 2nd/3rd team All-American if he looks back for the ball this season. Even though we lost Coleman, I was never very high on Anderson Russell (often seemed out of position, missed more open field tackles than any other DB) so IMO, having Hines and O. Johnson back there can't be too much of a drop off. Same corners, one brand new starter at safety and a potential All Big-Ten'er. Really not much of a concern to me.
Of course when your D-Line is stacked like ours, and our LB's are one of the best corps in the nation...you have to find something to be "concerned" about. :)