This question already has an answer here:
Alleged situation, due to X, country or geographical region Y falls off the internet map, but still has it's own network running. Blockchain splits and this situation continues for 6 months.
After 6 months there is a country specific chain, and the rest of the chain.
What happens, how can it be folded back in, does it permanently cause a chain fork, has this been considered or does bitcoin already handle this situation?