On one hand, I think you're right about Daryl because he is an incredibly stong, solid character secondary-but-central character (and also the harem of Daryl fans have threatened to riot if he dies off). On the other, I can see him dying in the very last season doing something heroic because I think what the writers have tried to communicate to us throughout the seasons is that in the end of the world, no one is the exception.

They've tried to build up the fact that the group is no longer ran by a single leader, but I don't believe it for a second. In a time of need, everyone still turns to Rick to make decisions, as was proven in the episode last night. He is the leader and he always has been. If he dies, the show ends, either by will of the writers or by loss of interest in the fans. I would not want to see anyone else lead the group and even though he isn't my favorite character, if Rick was killed I do not think I would continue to watch.

This whole show comes back to Rick because he is the one who's been there from the beginning and who much of the story has centered around. Fans grow to love the group as a whole and single characters here and there, but there is no other single character's experiences that allows fans to relate to as much as Rick has endured.