Many of the Chinese airlines are partially owned by the government, with controlling stakes. Which mean they have to follow state directives, including cutting reliance on Airbus and Boeing, especially Boeing. Any US ban can seriously disrupt China's civil aviation as what had happened to Russia's civil aviation.
I think you don't know Chinese government at all:
2ndly, a state-owned airline in China doesn't mean that government would cover its losses. Such thing indeed happened in Chairman Mao's time but not today, not after Deng Xiaoping's era. Otherwise China would have not jobless men because government would order state-owned companies hiring them all and communism would have been achieved tomorrow, or most likely, Gordon Chang would have become the greatest fortune teller in human history.
1stly, Chinese government worries C919 crash more than how many planes have been produced. Such prudence contributes a lot of C909/919's low utilization rates, but also contributes lots to their zero major accident record after all these yeas in service.
As for sanction, I have said in other posts that unlike Russia, China has means to make the West suffer if they do so. It's kind like: Why didn't Russian use nukes to stop NATO arming Ukraine?----Because NATO also had nukes; Why didn't NATO use nukes to stop Russia? Because Russia had nukes too. When you study a thing which involves 2 parties, you need to view it from both sides' angles for making the right conclusion, not only from one side's.