The group couldnt survive w/o Rick. I mean look who else is there to take his place:
Daryl: Badass like Rick, good shot, willing to take risks and do what needs done, survivalist, but he seems like a bit of a loaner, and is ultimately a better strong arm than a leader.
Hershel: Not as BA as Rick or Daryl, but a good shot, stands up for his beliefs, has the wisdom of age to make good decisions, but he's too soft.
Glenn: Smart, resourceful, but doesn't have the guts or the hardness necessary to carry the group.
Honestly, could Hershel or Glenn kill their best friend just to do what's best for the group?
Overall next to Rick, Daryl is the best bet.
And now that I've seen the end of S2 I think T-Dog should be off'ed. He doesn't do anything it seems.