It should be the same for Nat China. Szechwan falls, China can’t build no more whether they have 3 or more territories worth 3 icp’s or more.
If it’s liberated then they will get 6 icp’s and any non captured territories and can start building again.
If they have some money left and Szechwan is captured, they should have to give money to attacker. I would like to try this in a game.
The rule is as long as they have territories worth total of 3 icp’s or more, they can build and place in those territories.