Good response from "FH Alum" ...
A human can get 100% of their nutrition from vitamins, water and protein alone. Protein is necessary to rebuild cells, water is well-water, and all other nutrients can come form vitamins. A patient who undergoes bariatric surgery for obesity lives only on protein, water and vitamins. The patient can live a very active life including a large amount of exercise on 60g of protein a day, 64+ oz of water and supplements.
Granted the vitamins are not your basic Flintstone chews and are not inexpensive ($20/120 need 4 a day) but with something like Bariatric Fusion or similar brands available at most Bariatric surgery offices and online, a person could live indefinitely.
Protein bars are not the best choice for long term as a person with a normal stomach will be very hungry. (not starving or malnourished but hungry = unsatisfied) Psychologically, having to exist on nothing but bars for longer than a week would have a major impact. State of mind is key in survival.
For short duration periods however, they can be an excellent choice. I keep some in my winter car kit, disaster kit etc. A 20g. protein bar will provide the same as 4-5 ounces of meat or one meal. The trick is to find one that is low sugar. Sugar makes you hungry and wanting to eat more. Add a ration of vitamins, water purifying bottle, crystal light packets (or similar to mask bad taste of emergency water) and a person would be set.