Favre is simply unreplaceable and much like when a big time college coach retires (Spurrier or Osborn) the next coach or qb is a lame duck because the expectations and performance were so high with a qb like Favre.
Believe me, it's not something Packer Nation should take for granted. Miami is still feeling the effects of not effectively planning (and grooming) a suitable replacement for when Marino left.
Is Rogers the answer? No one can say. If I recall, GB only drafted him because 2-3 years ago Favre was tinkering with the idea of hanging 'em up. Rogers was the insurance policy. Now, the good news is that he has had several years to learn the system(s). He wasn't thrusted right into the starting lineup which is the norm nowadays (see Vick or Vince Young).
Having said all that, it was great watching Favre play. He made the game fun. in an era of system QBs and complicated schemes, Favre is/was the last true gun slinger at QB. He's a lock for the HOF and is on top of numerous passing stats.
He will be missed.
Erik