I actually think the depth at LB is fairly good. Preston Brown, Nigel Bradham, Keith Rivers and Brandon Spikes should be able to handle the 3 LB positions. In a pinch I think they could move Manny Lawson to SLB. I also think they'll be in nickel quite a bit, so you'll see 2 LB's more than 3.
Injuries happen, sucks it had to happen in the off season, but it's part of the game (usually during the season).
Oh well, get well soon Kiko.