The category above deadly is "non-encounter".That wasn't the question. The question is what should we call the category beyond "deadly"?
I vote "blood sausage".
What's the encounter category of a brick wall? You either avoid it, circumvent it or leave. What is the encounter category of a blizzard? You either escape, avoid, or die. You're not beating either in combat. If the fight can't be won, it's not really a fight.
Unless you're just trying to murder all your PCs intentionally. If so, that category name can't be printed on EnWorld.