Character Death (DMG)

When a character reaches 0 hit points, that character is slain. The character is immediately dead and unable to do anything unless some specialized magical effect takes precedence.
==Death from Poison==
Poison complicates this situation. A character who dies as a result of poisoning still could have active venom in his system.
Poisons remain effective for 2d6 hours after the death of the victim. If the character is raised during this time, some method must be found to neutralize the poison before the character is restored to life. If this is not done, then after the character rolls the resurrection survival check given in "Raising the Dead," he must immediately roll a successful saving throw vs. poison or suffer all the effects of the poison in his body, as per the normal rules.
This may only injure some characters, but it may kill other characters seconds after being raised!
== Death from Massive Damage ==
In addition to dying when hit points reach 0, a character also runs the risk of dying abruptly when he suffers massive amounts of damage. A character who suffers 50 or more points of damage from a single attack must roll a successful saving throw vs. death, or he dies.
This applies only if the damage was done by a single attack. Multiple attacks totaling 50 points in a single round don't require a saving throw.
For example, a character would be required to make a check if a dragon breathed on him for 72 points of damage. He wouldn't have to do so if eight orcs hit him for a total of 53 points of damage in that round.
If the saving throw is successful, the character remains alive (unless of course the 50-hit-point loss reduced his hit points to 0 or below). If the saving throw fails, the character immediately dies from the intense shock his body has taken. His hit points are reduced to 0. The character still can be raised in the normal ways, however.
== Inescapable Death ==
There are occasions when death is unavoidable, no matter how many hit points a character has.
A character could be locked in a room with no exits, with a 50-ton ceiling descending to crush him. He could be trapped in an escape-proof box filled with acid. These examples are extreme (and extremely grisly), but they could happen in a fantasy world.
As a general guideline, inescapable deaths should be avoided—characters always should have some chance to escape a hopeless situation, preferably by using common sense and intelligence. This maintains the interest of the players and helps them retain their trust in the DM.
However, if a situation of inescapable death occurs, the character dies, and there is no need to play such a situation out round-by-round. Allow the player to attempt reasonable (and perhaps even truly heroic) methods of escape. If these fail, simply inform the player of the demise of his character. The doomed character is assumed to have lost all hit points. 
==Raising the Dead==
Curative and healing spells have no effect on a dead character—he can only be returned to life with a raise dead or resurrection spell (or a device that accomplishes one of these effects). Each time a character is returned to life, the player must roll a resurrection survival check based on his character's current Constitution (see Table 3 in the Player's Handbook).
If the die roll is successful (i.e., the player rolls equal to or less than his resurrection survival percentage), the character is restored to life in whatever condition is specified by the spell or device.
A character restored to life in this way has his Constitution permanently lowered by 1 point. This can affect hit points previously earned.
Should the character's Constitution bonus go down, the character's hit point total is reduced by the appropriate number of hit points (the amount of hit point bonus lost is multiplied by the number of levels for which the character gained extra hit points from that bonus). When the character's Constitution drops to 0, that character can no longer be raised. He is permanently removed from play.
== Hovering on Death's Door (Optional Rule) ==
You might find that your campaign has become particularly deadly. Too many player characters are dying. If this happens, you may want to allow characters to survive for short periods of time even after their hit points reach or drop below 0.
When this rule is in use, a character can remain alive until his hit points reach -10. However, as soon as the character reaches 0 hit points, he falls to the ground unconscious.
Thereafter, he automatically loses one hit point each round. His survival from this point on depends on the quick thinking of his companions. If they reach the character before his hit points reach -10 and spend at least one round tending to his wounds—stanching the flow of blood, etc., the character does not die immediately.
If the only action is to bind his wounds, the injured character no longer loses one hit point each round, but neither does he gain any. He remains unconscious and vulnerable to damage from further attacks.
If a cure spell of some type is cast upon him, the character is immediately restored to 1 hit point—no more. Further cures do the character no good until he has had at least one day of rest. Until such time, he is weak and feeble, unable to fight and barely able to move. He must stop and rest often, can't cast spells (the shock of near death has wiped them from his mind), and is generally confused and feverish. He is able to move and can hold somewhat disjointed conversations, but that's it.
If a heal spell is cast on the character, has hit points are restored as per the spell, and he has full vitality and wits. Any spells he may have known are still wiped from his memory. (Even this powerful spell does not negate the shock of the experience.)