> If you see a [dead] post that shouldn't be dead, you can vouch for it. Click on its timestamp to go to its page, then click 'vouch' at the top. When enough users do this, the post is restored. There's a small karma threshold before vouch links appear.
I should revisit the guidelines and the FAQ sometime.
Also, here is a link that explains undocumented features and behaviors of HN for anyone interested: