I have seen whole countries "drop off the internet" for extended periods of time. Sometimes it is political, sometimes it is due to a cable break.

Russia has suggested dropping off the internet: https://www.technologyreview.com/2019/03/21/65940/russia-wan...

China has a fairly successful firewall and has recently come out against bitcoin mining.

I can see a country that feels that bitcoin threatens its currency working hard to create a bitcoin firewall. I can also see the firewall being lifted after a change in government.

If the country re-joins and its blockchain is shorter than the current chain, what happens to all the transactions? What happens to the coins that are mined within the country?

I can see where a country could have billions of micro-transactions (e.g. coffee purchases) that happen over a single year.

Is it even worth the processor time to process billions of "penny" transactions?