Comment by dang

Not deleted—we only ever delete comments when the author asks us to, and they show as [deleted], not [dead].

[dead] comments are readable by anyone who wants to turn 'showdead' on in their profile. This is in the FAQ: https://news.ycombinator.com/newsfaq.html.

In the case of the GP comment, it was [dead] because users flagged it. (I've unkilled it now though.)