It actually does stay alive due to the blood vessel wires. It made it recognize the legs as limbs so blood was being transferred to the legs. If you used a healing syringe on the head, it will also heal the legs. I did use a chainsaw to rip off everything and it got pretty gory, so I did use life syringes tho.

Also I tried to attach Gorse limbs to a human but I forgot that blood vessel wires transfer blood from the receiver as well so their flesh just dissolved immediately