Jumped ahead quite a bit because frankly this arc is already running long and I don't think the logistics of John getting the snacks or talking to Atropos about the bargain was worth the time.
They can recover from just about anything, including headshots, provided they have enough biomass to replace the lost body parts. But conversely they can be destroyed by any sufficient physical injury that exceeds that limit.
They can recover from just about anything, including headshots, provided they have enough biomass t