The issue with getting rid of Tillman for someone is that you fill up one hole only to create another. It really isn't necessary yet since he's proven he is still capable of playing at a high level.
Before letting Trillman go, I'd see how he was @ safety first. I believe he would be a great safety. Other good CB's turned have into decent safeties in the past. It's worth a shot, we always seem thin @ safety.
I wouldn't cut Peppers, I would ask him to restructure his contract. I wouldn't bring back Izzy, I would draft a DE in the 4th.
I would sign a CB in FA to go along with Tillman, Jennings, Frey, and resign Moore. Ask Tillman to restructure his contract.
I would resign Urlacher on the cheap. I would resign Roach and Hayes. I would draft a MLB in the 1st or 2nd. Keeping Briggs and Thomas also.
I think we are set at Safeties. Wright, Conte, Steltz, and Hardin.
That is a nice defense that is incorporating some good youth while maintaining older talent. The key would be having a rotation system where there are older players like Peppers, Briggs, Tillman, Urlacher and the DTs. Asking 300 lb lineman to play at a pace that we do, requires heavy rotation to ensure fresh bodies.