Carol and/or Beth dying is pretty high up on the probability meter. Reasons?
Beth: They actually develop her character with an entire episode devoted to her, which moves her from "omg stfu with the singing" to "hey, this girl is alright!" territory. Neglected characters getting tons of screentime out of the blue is always a warning sign that they might get bumped off. However, I still put her slightly lower on the death-o-meter, primarily because I can easily see them trying to do some Daryl/Beth/new kid from the hospital love triangle bullshit. If they do the whole Alexandria Free Zone plot, then the hospital kid will be key to that because he already stated in the show that he is from there (not by name, but by description), which means he won't be going anywhere soon.
Carol: Her character has actually evolved a ton since the show started...she went from abused housewife to a badass female Rambo. However, this season has been pretty Carol focused and we've been having lots of "fill in backstory" moments with her, which is usually code in a show for "lol, lets make them care about the character just before we KILL them". Considering the looming contracts for actors and the fact she is one of the few original actors from S1, she is very likely to die as a "omg! Noooo!!!" mid-season finale cliffhanger.