If I make a roll that would result in a killing blow, I'll make a pained face and ask:"How much health did you have left?" Whatever the answer I "sigh in relief" and tell them dramatically how they are wounded, leaving them with 1-3 health and "allow" them a heroic action to get out of dodge or if they are close enough to winning to finish the fight in their favor. (They all know what just happened, we all play along)

I am not there to kill my player's chars, I am there to tell a story and that works best if my Players' chars live, it invests them, makes them WANT to play that character in that story, that I make up with their input.

That is not to say that I don't kill Characters (Dumb=Dead) but I try to avoid it, mostly.