Instead of having a crippled Head result in death, I propose that it force the player to Sleep (getting knocked unconscious) for a certain amount of time. Obviously if the player was in combat at the time, sleeping for an hour while zombies are chewing on you will still result in death, but this might be significant for blood-loss related damage, accidents (vehicles, explosions…) fights where you have allies with you, etc. If you live long enough to regain consciousness, you could suffer various penalties for your concussion and/or fractured skull until your head recovers from Crippled status, like periodic vision and hearing problems, fainting spells, nausea, pain, extreme vulnerability to getting knocked out again, etc…
Basically what I’m saying is that my terrible demise should be drawn out and agonizing and filled with false hope, rather than a nice clean “you died, try again.” 
Overflow damage is already redirected if it hits a crippled limb, right?
Along similar lines, could there be an ability to nonlethally disable NPCs if you use unarmed or something like that? Maybe using the same script that reanimates zombies, and having NPCs drop an “unconscious body of X” that will reanimate in a certain number of hours, if you “kill” them with unarmed attacks?