I agree that Timbo and Seau are big losses, however, Zagonia is a great D lineman so the only thing we'll lose there is the rotation. Timbo is the better runstopper but I think we'll be alright.
Seau was really lighting it up but if Hendricks can just hold his own and not get beat, like maybe Derrick Rogers, again we should be ok. We will still miss the extra plays Seau made.
So maybe we won't be quite as lights out but the D should still get the job done.