This idea is actualy taken from primal carnage. If the rex eats you ,it will regain hitpoints in that game.
I dont think its that big of a job to make. It would only need a new final killmove animation and a healing effect.
Could be added to other monster races as well later on.
I find it very weird that creatures in Skyrim keep killing eachother for no reason at all.
Wolves usualy dont hunt rabbits just for fun..
Its important for immersion. At least for me.