You're several levels deep into a festering pit of evil when one of the party members bites the dust. No raise/resurrect magic is available. That PC is going to stay dead until you get back to civilization. What is the player going to do? Anybody who putzes around in dungeons long enough will probably encounter this problem at some point. Rather than have the player of the dead PC sit on his hands until their dude is breathing again, here are some methods for getting that player back into the game as soon as possible.
Video Game Style "New Player Added" - Just like playing Gauntlet, new PCs pop in whenever available. Not every campaign will sustain this kind of abuse, but it's the easy way out if it won't make people at the table wince. The World of Alidor campaign suggests a way to use this technique without bending the universe. In the Alidor setting the Elan (a PC race from the Expanded Psionics Handbook) simply pop into existence fully formed, as they are something like the solidified thoughts of giant tortoises. I'm not sure if they only appear close to the titanic turtles or not. If they can appear anywhere in the world, I intend to whip up an Elan psion as an emergency back-up PC.
The Prisoner - This one is almost as easy as kicking it Video Game style, but puts a lot less pressure on the suspension of disbelief. Simply chain up the PC in the next available room and stash their equipment in the next room over. (Just be kinder about it than my old DM.) Unreasonable players may try to glom onto the new PCs stuff before they re-equip. I avoid this problem by not gaming with those sorts of people.
Solo Adventurer - The party stumbles upon a lone PC that is willing to team up with the party. Works best if the new PC is a sneaky type like a rogue or can teleport, as it dodges questions like "How did your plate-clad warrior get down this deep without setting off an alarm?" Again, problem players may decide to exploit the situation to their advantage. ("I say we kill him. Our guys don't know he's a PC and have no reason to trust him.") But why are you even playing with jerks like that?
If you're going to use any of the above three options to beam in a new PC, make sure to plan ahead. DMs need to let the players know that dropping in a new PC is an available option and make clear to the players exactly how he wants replacement PCs built. Players need to take time beforehand to whip up a back-up PC. Even if you only use your new guy until your main PC is ressurrected, it would still behoove you to show up with another dude ready-to-go. That way you aren't wasting time during the session throwing together a half-assed character build.
If you don't have a back-up PC ready or if the DM isn't going to allow any PC paradrops, you still have at least one more option to explore.
Brevet-PC - Take an NPC already associated with the party and upgrade that character to PC status. This contingency was half the reason to have henchmen under older editions. A cohort makes a fine choice, but a role-playing oriented player may well have a good time playing a familiar or a follower. In my present campaign when Uther the Justiciar died in mid-adventure the player took his own cohort and re-statted him as a full-strength PC. It looks like Odolan the Ex-Cohort will now be a regular member of the team. Always look for opportunites even where no decent character is available but a raise dead is just around the corner. "Hey DM! Can I play the ogre that the wizard charmed until my fighter is back online?"