So I recently had this happen, one of my colonists had their waist cut off. This should obviously be a severely crippling or lethal injury but checking the wiki and how its behaving in the game treats it as no big deal or even anything other than painful. This might just be an oversight as from what else i have seen is that the waist has 0% coverage and shouldn't be capable of being hit in the first place. I saw these details mentioned in other spots and one more instance of this exact injury occuring but could not comment on the thread.