If you read TWD Facebook page, there are a lot of fans (male and female) on the borderline with the show. Killing Daryl off just might lose some of them.
There's many reasons why people watch shows and many reasons why people give up on them. There are several shows that I no longer watch that I used to really like. I just didn't like the direction the show went and I lost interest. At this point, if Daryl would die, I have no idea how long I would watch the show simply being that I don't know the direction the show would take. I do know that there isn't enough interesting characters on the show that if they kill them off simply for shock value, the show will suck. It's tv. If you don't replace interesting characters with characters equally interesting, when you kill them off, you won't have much of a show.
You have to ask yourself why they developed a non-comic character like Daryl to begin with. And like I said, unless Reedus wants off the show, I don't see them killing him. They might pull a Glenn for the season finale and leave you thinking he's dead though.
My bet is that a very pregnant Maggie or Judith is the one that gets killed. There could be some real shock value to those deaths (for those putting value on it).