PDQ in a Gritty Setting
Hit dice or tracks from other systems provide a quantitative means of determining health. It's helpful in that it helps you determine the overall status of your character. When killing a character in these systems, aside from special circumstances, you are required to exceed a damage threshold, which can take many rounds for high level characters to be killed.
In PDQ we have explicit/implicit options concerning the occurrence of death:
1) Characters can be killed once they are down/out (no roll required, just a declaration on intent to kill) (This is the Default assumption. A gritty setting would use killed once down.)
2) A Killing attack is declared with intent to kill and is successful (and is plausible given circumstances – game mechanics allow for this in combat)
3) Environmental Physical Damage can kill, “Continuing Danger” rule (useful in gritty setting)
4) Bleeding to death is possible. A blade across the throat will cause bleeding, but the results are largely based on intent and success of the attacker (or GM intent).
5) Accidental death is a matter of flavor for PDQ, and obviously appropriate for a gritty setting.
Sometimes there is a damage threshold, but PDQ does take the mechanics out of most of the death process. In a gritty setting it lets a player hold on to that last little bit of hope that maybe, just maybe, he'll pull through. Because in some systems recovery can take days or special acts from healers (very mechanical and unrealistic to me), but in PDQ, if the danger lets up a little, some recovery is possible (2nd wind) and the story can pick up from there.
In my Supers campaign, when a PC was attempting a violent act against another character, I would ask the player if the intent was to kill. So far, this has worked out very well. Though the supers campaign would not be considered gritty.