There is no "reprocessing", in Bitcoin the longest chain always wins. Assuming the cut-off country has fewer transactions than the rest of the world and assuming the people still continue to trade among themselves without any connection to the main net (which would be idiotic), every single transaction is invalid because it never was included in the longest chain. The only thing that happens when the country allows Bitcoin connections again is that everyone who accepted BTC as payment to a local wallet during a time when they had no internet connection find out they made a big mistake.
Look at it this way: Would you trade Bitcoin with someone on a private intranet? They tell you "give me $1000 and I'll transfer you the coins on my intranet, not on the public net". Of course you wouldn't, right?