It would only take one person smuggling a blockchain copy on a USB flash disk across the border to catch everybody up in censor-stan. Spending money (smuggling out transactions) would be a bit harder though; you'd have to get out a hibernated laptop with cached transactions or such.
The mining power of an isolated area would be much less than the rest of Bitcoin, they would only need to know to not trust payments in any locally mined blocks if they happen during isolation.
Deepceleron's razor #17: If something is worth saying to a noob, deepceleron has probably already said it.