China's one child policy means China has had a particularly low fertility rate for decades. Even now, it's "up" to 1.6. That's lower than Russia, which is far from replacement level. Child policy only takes effect after something like 20-25 years. So China's population will be well into decline before the first effect of canceling the one-child policy will be observed, in 2030-2035 (2010 - 2015 + 20 years).

Additionally Health services in China don't match those in the West, so they will lose people far faster.

China is in a much worse state than even Eastern Europe when it comes to population. It doesn't look like it, but China went into decline 3 years ago and will not stop declining until at least 2060. And it will be quite a steep decline starting in 2030 or so.