Milenia of failure. None of their dinasty's lasted even 1,000 years and many where very short.
No civil war destroyed all records. No civil war spanning more then three generations. No locked in against foreigners syndrom.
If China does undergo civil and political upheaval I don't think it has the social institutions or mechanisms to suddenly switch to enlightened liberal democracy, history matters, but that doesn't mean the Communist Party is guaranteed political control in perpetuity.
It got pretty damned close in the Cultural Revolution.