For me, it depends on the game I am running. If I'm running a classic module at Gary Con, I bring 2x the # of players as pre-gens. If there's a death in the first 75% of the game, they get to pick from one of the other pre-gens. If the latter quarter, dead is dead.
For my Orc themed games, I don't run as seriously as I would other games, so I let them respawn, even in the final act of the game.
Either way, I try and do right for the players. They chose my game for one reason or another and it's important to me they enjoy themselves. I've been in con games where somebody dies in the first 30-60 minutes and they've been told they're S.O.L. by the DM.