Being very different from other fantasy based MMO's, being 'resurrected' at some nearby location or via some spell or scroll just doesn't fit.
So I'd liketo suggest something 'similar' to the way Wasteland handled this, but adjusted for the Fallout world.
Wasteland = Damage -> unconsciousness -> seriously wounded -> mortally wounded -> DEAD (* permanently)
As a player became progressively closer to death it took a higher medic -> doctor skill to heal/revive them. Unconscious players had a chance to revive on their own provided their injuries/conditions weren't too bad.
Now, of course permanent death in an MMO would svck. It would pretty much mean character deletion and starting over. That would be lame.
Alternative: DO-OVER -vs- hardcoe modes.
hardcoe = permanent death but if you make it through the game in HC mode you get a nifty reward like a rare item or a medal/title/achievement or something.
DO-OVER = You return or 'flash back' to the last town you were in before leaving to travel, or do the quest/mission. You lose all loot/xp/money gained since leaving that town and must start the quest or mission or trip over again. The price of failure = your lost time but at least you learned a little bit from it and will be more likely to succeed next time you try.
As in Wasteland, if at least one party member survived and had decent medic or doctor skills they could revive the entire party. But once everyone in the party is beyond unconscious you're going to die.
Also...In Fallout there was the 'Mysterious Stranger' perk. Maybe this concept could become a possibility for a random caravan of travelers to find and revive you as well. If you see Metal Maniac, let him know I'm looking for 'em.