DEATH IN THE CAMPAIGN - D&D CYCLOPEDIA

If you want your campaign to behave more like the fantasy stories you read or see in the movies, you might get rid of spells and magical items that bring people back to life. This includes spells such as raise dead, raise dead fully, reincarnation, and clone. This makes the campaign a lot more dangerous. When a character is dead, he's dead. The player characters will be a bit choosier about the fights they pick, and will run away from fights more often. High level characters will be rarer, as bad luck and player lapses will take a higher toll. This option gives character death more impact. It should be a sad and momentous event when a character dies—not just a delay in the proceedings. At best, it sharpens the players' perceptions of how mortal their characters are. At worst, it leads to general player dissatisfaction. It is not recommended unless the players are mature enough to handle losing a favorite character. 

Keeping Characters Alive

If you decide to get rid of the resurrection spells, you can also adopt another rule to make it a little harder for characters to die. For instance, when a character is reduced to 0 hit points or below in combat (or from death spells), he's not yet dead. He's unconscious and mortally wounded; if left untended, he will die. He must make a saving throw vs. death ray every turn. He makes the first roll on the round he drops to 0 hit point; he makes another every round he takes additional damage, and every 10 minutes (one turn) in addition. If he ever fails a roll, he's dead. If he keeps making his rolls until reached by a healing cleric, someone with the Healing general skill, or someone with a healing potion to get to him, he can be saved. If the healers can heal him up to 1 hit point or more, or the Healing skill roll is made at a penalty of -5 (regardless of whether it heals him up to positive hit point or not), then the character is alive. He's critically wounded—but he'll survive.