The current story arc begins at Strip 197
August 15, 2003
The first tag-line C&A had was "Mad scientist roommates who periodically die!"
I've never wanted to explain why they don't stay dead. To do so would ruin the humor of it. The prevailing theory from readers seems to be that since Andy is dating Satan, she keeps bringing him back to life. Casey gets in on the deal, being Andy's best friend and all.
But I can tell you that I don't subscribe to that theory. Remember that Casey and Andy died several times before ever meeting Satan. Also, we have several times seen her welcome them in to hell.
So whatever your theory may be, it's as good as anyone else's because I have no explination for it, nor do I intend to come up with one. :)