I'd agree with what I think Kevin is saying: given this somewhat unrealistic situation, as an Aikidoka that skilled would not be in that cornered do-or-die situation to start with (no offense Ian, but are you at the level of 'touch of death' that Michael described), then the only somewhat skilled might have to choose killing to save himself, the truly skilled would be able to subdue his attacker (perhaps without a punch--recall the drunk on the train story, empathy with the assailant overcame his belligerence) even if if meant being open to his attacker. That fear is what would drive the Aikidoka to kill rather than use a technique that would not kill. Those who are afraid and/or unskilled would choose to kill, because they lack the skill or courage to not kill.
Applies in the modern world as well as the unrealistic situation, as well, Michael. And the 'touch of death' techniques exist only in The Simpsons and Bruce's version of reality.