Or just not die at all! It's a terrible user experience to let people do things that cause the site to "die" in any way. We should handle it, even if that means putting a limit on thread depth. "Sorry, comments can only thread 50 levels deep."

(Which is terrible, and I am not proposing at all, I'm just saying -- it's better to stop the user before they blow things up, and even better is to actually deal with the blowing up problem.)