It's not a connection if you have separate tickets. So if you miss your flight, it's no different from oversleeping and getting to the airport too late.

What do your fare rules say about rebooking/changes, presumably after the outbound portion of a RT has been flown? Or do you have a one way ticket on Air China? I suspect that it's either a fly as ticketed or lose all value fare or one that permits changes if fare class is available for a fee (or for the fee plus payment of fare difference if inventory isn't available).