Your challenge, should you come to accept it, is, with a POD no earlier than 400 AD, produce a world in which the Chinese Language Family is completely extinct. Your scenario can include any of the folowing.
1) Northern China becomes Mongolian, Manchu and Korean
2) Use of any of the rivals of Chinese, Formosan(and Mainland Austronesian languages), Thai, Kadai, Miao and Tibetan etc.