If a person was unable to absorb nutrients from the large intestine, would this be lethal? What about if one could not absorb from the small intestine? (Anatomy and Physiology)

It would in fact be lethal. The main function of the digestive system is just that, to digest food. Both intestines play an important part in the digestive system (to digest and absorb all nutrients possible from stomach contents) The function of the large intestine is to absorb water, left over nutrients from the small intestine and, electrolytes. It would be equally if not more deadly if the small intestine couldn't absorb nutrients. Since the small I intestine also plays an important role with providing the body with nutrients and other vital materials it would be deadly if you could not absorb anything. You would go into a state of malnutrition and would need to be treated immediately.