Comments become dead due to user voting and can also be resurrected if people vouch for them.

I usually read the dead comments and occaisonally do vouch for them if I feel they were constructive and accurate but unpopular.

There is a seperate system of flagging comments which does usually lead to moderator review amd potential account action.

It is extremely rare for me to see a flagged and dead comment that doesn't obviously merit it.