They would be unable to do business in any real way with the rest of the world. They'd be communicating by landline phones, couriers, and carrier pidgeons. They'd just manage to get a 80486DX at a whopping 20MHz.

Some internet, but no HTTP, and likely no modern standards. Just how do you expect them to be a global center of trade in a world economy where their competition has modern computers, communications, and logistics?

Throw out their financial services industry and import/export businesses.

The advantage they're left with is the unique relation they have with China, where they have access to the market but don't have to play by the same rules. There's always value in legal privileges. Much of the world economy is driven by such privileges. But that's not an argument against the value and power of technology to create wealth.