If there is absolutely nothing else sustainable in a distance that can be traveled by (I am assuming) foot, then if it came down to it... those who are to survive are the ones who will adapt to their conditions. Survival of the fittest. The weakest ones are going to start getting picked off. But I have a hard time imagining that it would be emotionally possible to even do it. Killing a person would be one thing... difficult by any person of sound mind. Eating them afterwards?
In any situation like that though it is very unlikely that there would be no vegetation or wildlife around to sustain you.