That situation is referred to as a "Black Swan" here in the forum.
The market-peg of bitasset relies on the fact that you can always have your bitCNY exchanged for 99% of its value in BTS. If the value of the collateral drops too low, this guarantee can no longer be upheld. At that point, the exchange rate for settlements of that bitasset type becomes fixed. This has already happened to some assets, the most prominent probably being bitGOLD.
We're currently working on a process that will allow to "revive" bitassets after such a "Black Swan".