I did some research into the lethality of various injuries a while back. This mostly involved killing hundreds and hundreds of peasants.
My finding IIRC:
Any brain injuries:
Instant death - although i seem to recall an instance where a creatures brain was bruised and it was not killed.
Decapitation/bisection:
Instant death 100%.
Spilled guts:
Certain death by bloodloss.
Throat, major artery torn:
Certain death by bloodloss
Heart, major artery torn:
Certain death by bloodloss
Heart, bruised:
Causes Mortal Wound notification, however it is non-lethal
Lungs, bruised:
One lung results in becoming winded
Both lungs result in suffocation
Lungs, torn:
One lung results in becoming winded
Both lungs result in suffocation
Spinal injury:
Upper: Death by suffocation
Middle: Death by suffocation
Lower: Lower body paralysis, non lethal.
Loss of limb:
leg upper, lower: very lethal. if it was the only injury subjects had a chance of living, however any other bloodloss suffered on top of this would generally result in death.
arm upper, lower: not as lethal as a leg, bleeding tends to stop rather quickly but still very deadly.
feet/hands: heavy bleeding, not essentially lethal.
Organ damage:
non lethal, at least in adv. mode. I have heard reports of liver damage causing prolonged death and stomach damage causing starvation due to vomiting, not useful for combat.
Skin damage:
light bleeding, non-lethal
Muscle tissue damage:
moderate bleeding, non-lethal depending on extent.
Bone:
Varied, bone chips, fractures, shatters cause extreme pain. Broken bones can be jammed thru organs/tissue causing further damage/death.
Non-major arteries:
Heavy bleeding, not necessarily lethal.
Tendons:
Non-lethal, results in loss of motor control.
Nerves(non-spinal):
Non-lethal, results in loss of motor/sensory control.
Strangle:
IME it is non-lethal and will only knock creatures out. However it is a good way to KO your opponent for a coup de gras.