The most recent Chinese, 25 year demographic forecast (population data, projected to 2048) estimates a Chinese population of 620 million, in the year 2049, a -56% decline! (... officially termed: "a catastrophic collapse" - as opposed to just a "demographic contraction", for obvious reasons.)
There could be found only 3 similar instances (such as: Egypt, "New Kingdom", etc.), in documented human history, where following such a population collapse, confined to a specific geographic region,during a proportional time interval, eventually resulted in a partial or full recovery of the local (indigenous) population - i.e., extinction avoidance. Placing the odds for a 5th Mllennia for the Chinese civilization/empire significantly below 50%.
Furthermore, the technological status (advancement level) of the state, at the time of the collapse, is inversely proportionate (power law) to the resulting fraction of the remainder of the population. (The "more advanced", the less likely to survive/recover, dependent on the speed of decline - most likely due to increased segmentation/specialization and the resulting sudden, irreplaceable voids in essential products and services.)