It is railroads and not oil which enabled Switzerland to import so much food. The country imported food before the combustion engine became a factor and I don't see why it should stop importing food because of a decline in oil production.

Of course ... as long as the food exporting nations still are able to produce a surplus that they are willing to sell.

Food shortage will not become a problem immediately here in Switzerland, because there is more elasticity in food production than in energy production. When the times get harder and people have less money, they'll reduce their consumption of meat and turn to eating more of the cheaper food items, like potatoes and bread.

As the demand for meat shrinks, the sizes of the herds will get reduced, and more vegetables will be produced instead, thereby increasing the ability to feed more people.

If Switzerland had to feed itself for some reason, people would of course have to emigrate (as they used to do back in the day). Racist pogroms (how do you tell a foreigner from a citizen?) wouldn't be sufficient considering the likely magnitude of that shortfall.

I hope it will never come to racist pogroms, but people aren't rational. Whereas each individual person is open to logic arguments, masses rarely are. In times of hardship, it is natural for humans to turn around and look for a culprit to blame. The Swiss are no better than other people in terms of xenophobic tendencies.

But how useful is it base one's reasoning on national boundaries really, especially in the heart of Europe?

It may be neither "useful" nor "rational," but in times of hardship, people remember their roots. National identities become stronger, not weaker in such situations.

This may have negative consequences (like in the case of racist pogroms), but it is not purely negative. It gets neighbors to band together and help each other out.