Well the thing is, the engine/game assumes that once a target has it's limb blown off, it's dead, so when you shoot a guys are off, the game forces him to die.
I think they ought to have a death timer. A bit like in RDR, but better
Head blown off (Instant death)
One shot to chest (Without armor) Knockdown, but shooting from ground. (10 game minutes until death)
Two shots to chest (W/O armor) knockdown, no longer shooting, crying/screaming/cursing (5 game minutes until death)
Three shots to chest (W/0 armor) instant death.
Arm(s) blown off: (Death within 10 game minutes (roughly 10 seconds) unless shot again
Legs blown off (same as arms) unless shot again.
(Multiple crippled limbs that were not dismembered could cause them to lose consiousness with a 20 percent chance of dying while unconsious.)
Until Death they can crawl, cry, scream in agony, Beg for help (With a high doctor skill you could use "Mercy Healing) and save them for good karma and they will no longer be hostile (Only with some, others will turn against you. A mercy killing will also net you minor good karma, while letting them expire in pain will cause minor bad karma, but neither will affect reputation further) curse you. This is the kind of Fallout Game i want, and wanted since fallout 3. I know it isn't in NV, but PLEASE BETHESDA/OBSIDIAN for GOD'S SAKE, put it in 4! It would be such a realism improvement...In the mean time...I smell a mod.
This is all assuming Fallout 4 runs on a new, more powerful engine.