[defrost]

I won't quibble with your if the world goes nuclear scenario here but I would ask; how lnog can Mauritius self sustain without outside trade for fuel and food reserves?

It's an island that grows some food, of course, but how much relative to the population?

[chalcolithic]

It definitely is not self-sufficient when it comes to food. But trade routes are pretty low tech things, we've been having them for thousands of years, I expect them to reappear quite fast.