What if there was no one to offer food to monastics? This is a questions that often comes up when I visit study groups, particularly when the subject of everyone practicing like a monk/nun comes up. Wouldn't monastics be allowed to farm-just enough for sustenance?  It seems extreme that they would just starve because no one fed them. My understanding was that the food offering was mostly established for the lay people to have an opportunity  to give and gain merit, but I may be wrong. Is there a canonical reference saying monastics can only eat if given food? What did they do before the order was fully established? What about forest monastics who go of for extended periods alone?
There are several monastic orders that currently allow monks to cook their own food, but usually there is a lay community that donates the cash or food.

I don't know of anyone who starved merely because there was no one to offer food. The Vinaya is real but so is reality. I think most will find an empty stomach is more real than the Vinaya.

In any case the making an honest living, if absolutely necessary isn't a parajika offense - a monastic may prove to his/her peers that it was essential to earn money, and if the peers agree, there is no penalty. Even if it is found to be an honest mistake, it won't be treated as harshly as if one had broken a parajika vow.


  The four transgressions which incur a Parajika, the penalty of
  automatic disrobal, are as follows:
  
  
  Engaging in sexual intercourse with another being of either sex.
  Stealing something of value (which includes smuggling, cheating or deliberately avoiding payment of a tax).
  Purposely killing a human being or encouraging him or her to commit suicide (this includes inciting another to murder somebody and it also
  includes convincing a woman to have an abortion.
  Boasting that one has realised a high spiritual attainment, knowing that one is lying. For example, claiming to be enlightened, to be
  Maitreya Buddha, to have entered Jhana (deep meditation-ecstasy) or
  that one can read minds when one knows that one hasn't reached any of
  these states.
  


source: http://www.budsas.org/ebud/ebsut019.htm