What happens to the ETF when a stock in it gets delisted?

It depends on the type of ETF. If it is a passive index tracking ETF, the delisted stock probably drop out from the index and the ETF will follow suit. If it is an active thematic ETF, then it is up to the ETF manager discretion to replace or redistribute.

It will based on the market cap of the companies and re-distribute. Eg. S&P500. If 1 down, another one must come in, else become S&P499.

Scare china stock delist? Me too.😅​​​