What happens if the Internet goes down?

If internet goes down, big problems arise. Bitcoin won’t be the main concern. But let’s say power stays somewhat intact.

If miners can’t communicate, they’ll just work on isolated chains. That’d be a messy situation.

Wait, difficulty and old addresses? I don’t get that connection. Can you break it down?

They still need to create valid blocks or they’re rejected by full nodes. I might've misunderstood your point earlier.