Depends on which ones. If you're going for the big names, many of them are dual listings, meaning that they have HK listed shares as well. For some, the US listed shares are fungible, meaning that they can be exchanged for the HK shares at a certain ratio. For example, Alibaba, trades under 9988.HK on the HKEX. BABA can be converted to 8 shares of 9988.HK. The conversion will likely incur a cost (dependent on broker).
For those shares which do not fall into this category, they will be delisted to the OTC markets and will continue trading there. However, do note that OTC markets tend to be less liquid which may cause drastic price movements at times. Tencent's shares are actually already in the OTC markets under the ticker, TCEHY.
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