Main cast die all the time, Terri Bauer, Nina, Sherry Palmer. I think Michelle and Palmer are dead.
Now that I look back on it, Killing Teri Bauer was the best decision the show made. They said that it was 50/50 that they were going to change the ending of the first season so she lived, but they went with her death. Having her alive would have limited the show incredibly.
I agree on palmer, but after tony felt for pulse it was as if he almost made a sigh of relief and he did not attempt CPR wich I think he would have if she didn't have a pulse.
Ryan Chappelle in season 3 was actually turning into a sympathetic character and redeeming himself. That was the most painful one if you ask me.