You can vouch it, and if the comment is still [dead] but it's really good you can send an email to dang and tomhow hn@ycombinator.com Remember to include a link to the comment, and use it sparsely because it's a manual processes.
Like the parent commenter, I frequently see high quality posts via showdead. I vouch them, but I've never seen one resurrected soon after. I rarely remember to go back and check hours later, but by then the thread has died down anyway.
It takes a few vouches to unkill a comment. (The exact number is a mystery (I don't remember dang telling the number ever) and it may change from time to time (or not).)
For not-bad comments just vouch them, but for very-good-I-will-not-be-able-to-sleep-until-it-is-unkilled comments vouch and send an email.
