It may of course be utter rubbish, but let's say the Chinese government does block internet access to the blockchain itself.
The blockchain is a data structure, not something that people access over a network. The Great Firewall can block nodes from connecting to each other over the internet but that does not prevent nodes from accessing their own local blockchains. They are blocking access to other nodes, not to the blockchain.
As TOR seems very hit and miss there
How so? AFAIK TOR is fairly reliable and can easily get around the Great Firewall. Bitcoin Core (and anything based off of it) has support for connecting over TOR and even allowing incoming connections over TOR with automatic hidden service creation.
and VPNs are slowly being hunted to extinction
I don't think the Great Firewall can kill all VPNs. New ones will constantly be made.
what would be the options for a Chinese person who wanted to interact with it?
They can get the blockchain data and send and receive transactions through non-internet related methods. They could use the blockstream satellite protocol with just normal radio stations on the ground and use that to broadcast out of China. Data could be transmitted over websites and other non-Bitcoin protocol things. The problem is not about China blocking the Bitcoin network; there are always ways around that block even though they will have higher latency. The problem is China banning Bitcoin mining as that will essentially shut down all mining operations in China which consists of a majority of mining on the Bitcoin network.
Does the Blockstream satellite thing work?
Blockstream satellite is currently only one way. You can only receive blocks from it. They are working on expanding it so that more of the world is covered and more stations are set up. What could happen is that an uplink station in China is set up and the Chinese miners can send their blocks to that station to be broadcast to the rest of the world. And maybe you could then send transactions to that station to also be broadcast to the rest of the world.