Assuming a Meteorite hits New York

all banks in the USA may see their ratings downgraded. That seems to be the logic behind the thinking that causes Tom Brown to decry the latest 'nonsense from the rating agencies'. Banking as it is conducted at present will always pose a certain amount of risk - only 'limited purpose banking' that turns banks into a sort of mutual fund would avoid any risk of failure. As a consequence, war games based on worst case scenarios may be of intellectual interest but they also undermine the credibility of rating agencies.