An attribute I created is DIV, which stands for Divine Intervention. It is a fail safe of sorts to prevent players from doing something stupid that kills their character off and thus ending the game for them. A regular 3 dice attribute. SRs missed against it take off the number missed by permanently and render the person unconscious. It's sorta like an invoking of the Gods to save me as I hurtle down a bottomless pit.
I came up for the idea while doing one of the T&T solos. I had missed a SR and it said tear up your character, they are dead. Reading the other option I saw even at the worst damage the trap could do, I would've survived. Plus it would suck when friends came over, spent the time to make a great character they liked and within 30 mins of playing have to say, you died. Go home.
I'll hurt their characters, maim them, curse them and have really nasty thing befall them but it takes a lot for me to downright kill them especially after years in the making. Of course I don't tell them that-make it just near death enough to keep it exciting.
I think a lot of people use Luck in this context. A not unusual houserule is to allow a last chance save against death at the cost of 1 point of Luck.
I also gave Fate points to my solo delvers - 1 per level and 1 per solo completed. I allowed them to be spent on back tracking a fatal choice, or succeeding at a save or die save. Once spent , only gained by earning more levels or completing more solos.
There was also the Mega Death Saving Roll. If the Characters is "Dead" they get one final SR but it is at a Level that will require a double to pass. If they pass their Con is on 1. and the game goes on.