I remember that Fallout 3's Dogmeat took forever to heal back because he had soooo many hit points. I tried a few mods to prevent instant heal but never got it just right. It was made worse because I was using the wonderful Project Nevada and stimpacks healed over time. I admit I would make them essential but it did drive me up the wall, when we would have a hard fight and was low on Stim packs and they would get up and instantly be back at 100%. The one thing I'm hoping for no instant heal on companions.