It is not just China but countries like India, Brazil and Indonesia which would have become economic superpowers by 2050. As per the PWC report on World Economies China and India will be the top two economies with a combined GDP of 103 trillion USD in 2050. United States will be the only western power to be in the top 5. ....Countries like UK, France, Italy will not even feature in the Top 10. ...So that will change the game....However I agree with you that China would'nt be able to replace US and the World would be multipolar. China also face issues related to demography.