The people building that intranet are making heavy use of resources that aren't hosted within the country, some of which require circumventing the Great Firewall (e.g. tensorflow.org is hosted on Google infrastructure and therefore blocked). Some companies even use Google Docs in their hiring process to filter out candidates who can't evade government censorship.

Completely cutting China off from the rest of the internet would certainly lead to infrastructure outages and put all development on hold until mirrors for the necessary services are set up.

And that's just the tech industry. If a gadget manufacturer in China can't be reached to order gadgets, they might just as well not exist. Without communication, international trade breaks down as well. The outcome would be equivalent to sanctions on all Chinese-made products, which no country is willing to try due to how much it would hurt themselves.