It is true that China's population begins to decline soon, but the 480M by 2100 is nonsense. It peaks around 1.46B around 2030 & is still 1.06B at 2100. See populationpyramid.net .
Mr Yearwood makes the key point here: like Japan & Europe, China must accept immigration IF it wishes to sustain its population (& hence domestic economy). It is worth noting that soon after 2100 Africa surpasses ALL of Asia (including China & India of course). Africa is VERY large, but will still produce migrants the old world needs. This is merely population redistribution. What we do not need is schemes to make more local babies.
The one-child policy & its predecessors had little impact on the trajectory of Chinese population growth. As in all other populations, that is determined mainly by education of females, secondarily by lower infant & maternal mortality, longer life expectancy & increasing per capita income. Demographics, not policy, dominate population dynamics.
No need to worry about major wars either. A little calculation shows that the 60 million or so killed in WW2 was less than natural population growth in that period. No war until now has significantly slowed population growth.