In a typical Casa setup, the user is instructed to store their keys in separate locations to protect against key loss in case of a disaster, such as at home, their office, and a bank vault. If any one of those keys survives, the user will be able to recover their funds. However, in case of a disaster that destroyed a whole city (nuclear bomb or conventional bombardment, exceptionally large earthquake, tidal wave or major flood, etc.) all three of the keys might be lost.
For exceptionally large balances, store one key in a different city / state / country.