Death is defined by Wikipedia as "the permanent termination of the biological functions that determine a living organism."
Personifications of Death Edit
In some continua, death takes the form of an anthropomorphic personification, as in Discworld, Sandman, and Jack. Usually the personification is robed and hooded and carries a scythe, as in archaic Real World imagery. As it is impossible to make the personification of death itself forget anything like a living being can, most death personifications probably know about the PPC.
Death of Canon Characters Edit
Canon characters are bound to their home continua. When they are killed in badfic, they do not actually die—though the influence of the badfic has convinced them of their own deaths to the point that they cannot be distinguished from corpses. Canon characters killed in badfic can be brought to Medical for resurrection, possibly after being stitched back together or otherwise reshaped into something a little more compatible with life.
When a canon character dies as he is supposed to die in canon, he remains dead. Characters who are saved from death by a Mary Sue or other badfic phenomenon may experience the sensation that they should be dead—an uncomfortable feeling by all accounts. Such characters usually snap back into their proper (deceased) state after canon reasserts itself.
Death of Original Characters Edit
The success of an assassination mission is determined by the death of the Sue or Stu. This is why Jay Thorntree and Acacia Byrd were called up to the Sunflower Official's office after handing over Arwen Sue to the Discworld elves; because the Disc's elves take their time with their victims, she showed up on surveillance as technically still being alive.
The assassination of a Mary Sue is the most important element of returning a Suefic-affected canon to its proper state. In some cases, only the assassination of the Sue is required; in other cases, there are also OCs, Cute Animal Friends, or multiple Sues to deal with.
It is sometimes possible to rescue a non-Sue OC from a death that should have occurred in his home fic. Such characters are usually recruited into the PPC. They may suffer flashbacks regarding their deaths.
When a Mary Sue is scheduled to die in her home Suefic, this death must (oddly enough) not be allowed to occur. A Mary Sue who is allowed to control her own death will usually die very dramatically and almost always in the form of a sacrifice to save her lust object. If she manages to go through with it, she removes the PPC's main strategy, as it's rather difficult to kill someone who is already dead. A dead Mary Sue who dies on her own terms is a bad thing: using the power of badly written melodrama, she imprints her influence into the canon in a way that is exceedingly difficult to remove. Therefore, PPC agents are advised to kill the Sue before she has a chance to make her "heroic" sacrifice.
Death of PPC AgentsEdit
When PPC agents die, they tend to stay dead. One reason for this may be that most of them are more akin to canon characters dying in a way predetermined by their author than they are to OCs being killed off in a continuum not their own. Most PPC characters adopt the PPC as their home continuum when they join. Those that don't, especially those belonging to their own original canon, are more likely to retire back home before they die anyway.
Another, arguably more important reason is that Medical, DoSAT, etc. simply won't resurrect an agent dumb enough to get killed. There are various theories about why this is so, but when you get right down to it, it's a feature of agents not being Sues. If agents could be resurrected every time they got killed, they would be too powerful, and it would ruin the PPC's credibility.
A few resourceful agents have engineered their own resurrections without the help of HQ, but these are (and should be) few and far between. It's much better if they simply avoid dying in the first place.