It seems if enough users flag it gets killed instantly.
If not enough voters flag it might still catch Dans attention and he might manually kill it.
If a comment is dead we (users with over 500 points I think) might still revive it if enough of us vouch for it.
I'm not sure if we can revive a comment after Dan has used the banhammer.
Also I can confirm that unlike what someone thinks we who flag and vouch are not an elite group.
After 500 you get downvote and I guess vouch as well. You don't have to apply it anything, at least I didn't have to with the accounts that had those privileges, and I don't know anyone important around here, I'm just a bored sw engineer currently located in Northern Europe.
It's even less ‘elite’ — I have < 500 points and see a ‘vouch’ link on dead comments. The FAQ doesn't state the exact threshold; I'd guess it's 100 (at most).
It's not just one person normally. Not only you can click "flag" and find that no change was made, you can also vouch for flagged posts to make them visible again.
Is there any mod review that takes places before (or after)?