I think people generally interpret the word "guarantee" in the wrong way when it comes to stuff like this. Even prior to this latest twist in the story, people should never have seen it as a guarantee in terms of absolute certainty, but rather as an assurance based on trust. Insolvency has always been a possibility. Regulatory shutdown has always been a possibility. Saying that it's guaranteed does not negate these possibilities. Tether are a company who have made a promise to their customers. That's it. Promises can be broken, as appears to be the case now that it seemingly isn't backed 1:1 by USD.