Sure, even in North Korea with "Juche" (1) extreme self-reliance, there is some domestic consumption. Of potatoes, even (2). It's not that domestic consumption will go to zero.

But the point is that domestic consumption is not constant. It can decrease, it can substitute more basic goods. Such as potatoes.

1) https://en.wikipedia.org/wiki/Juche

2) https://en.wikipedia.org/wiki/Potato_production_in_North_Kor...