Except these stable coins doesn't solve the core problem cryptocurrencies do: uncensorable transactions. Tether for example has the ability to freeze addresses. They can also freely manipulate the coin supply (a necessary feature for stable coins) which goes against the decentralized idea of cryptocurrencies.
It has a global settlement (which more or less liquidates all collateral). It doesn't freeze the ETH blockchain that DAI are traded on. DAI could be returned to the main contract for X amount of ETH based on the spot price of ETH when the global settlement is executed. But DAI could still be traded around independently of the global settlement. It's value might have slipped as a result, however, based on whatever ETH became worth following the settlement. The market would still determine that price, however.
