The injury to Kiko stinks but I think there's a silver lining: Bradham and Brown will get good playing time and this year could be a jumping off point for a LB group that leads this defense for many years to come. Rivers and Spikes are good short term solutions that will help us absorb the impact of Kiko's absence this year, but Kiko, Bradham, and Brown are the future.
Look at the 04-06 seasons for the Chicago Bears:
2004 - Urlacher plays mostly injured meaning increased playing time and development for Hillenmeyer and Briggs (both drafted late in 2003).
2005 - Urlacher wins DPOY.
2006 - The Bears go to the Super Bowl and the LB group is considered best in the league.
I know there are holes in this logic (mainly comparing Kiko to Urlacher), but I really think we are positioned for long term success at the position.