You are entirely wrong. They simply wear 'missing limb' clothes.
^ Which in theory would work but would require lots of mesh work, and armour mod patches, and npcs would still use the lost limbs.
What it requires is someone with that talents to do http://www.youtube.com/watch?v=TDW1cEitYd8, as for setting it up its fairly easy the biggest problem I had doing this for FO3 NPC's (Yes, I did already create the crawling animations for NPC's) was the sheer volume of Armor mods and the near impossibility of getting this to work dynamically with all armors -> I do know of a way !!! but the functions required do not exist in FOSE and will not for FONV -> I created some tests some time back that did some slight scene graph manipulation to flip the Cull Flag on leg and arm partitions on armors while worn the problem is I am not the SE guys and have no where near the coding expertise to get this to work consistently without crashing the game and causing all kinds of havok -> I was able to get a kinda functional dynamic armor Body Part Culling but the Changes applied to base references so every item got the culling and a secondary problem the armors needed to be unequipped -> re-equipped for the changes to apply and creating the second NPC to look like the first was a pain in the A$$ as the Match functions hated working consistently.
If the SE guys add some functions that allows you to cull body part partitions on a per actor basis without actually altering armor base references or actor base references -> and if Resurrect 1 actually works this time around I will do this for NPC's as its something I have wanted to do since playing Dead Space !
EDIT:
Actually now that I think about this more the very last thing I want to do is to do this the same way I did it for Feral's so I would also need NVSE to have OBSE's ToggleSpecialAnim ported over along with Get/SetBodyPartPartitionVisibility 0-14 0/1 (1 = Visible when Alive, and 0 = Visible when Dead) along with Resurrect 1 working properly or some way to clone actors as using Factions and Match Face to try to get a clone was a royal pain in the A$$ for FO3.
Also Porting over Event Handlers so I can attach the script to actors as they die instead of the insanely incomaptible method of needing to attach them through scripts attached to every individual actor or using some explosion or ref walk to apply an effect -> which I would prefer not to do long term.