Can the government confiscate gold kept in a bank safe deposit if the bank fails?

Yes. The Government can confiscate any property that belongs to the bank that failed (including buildings, gold bars and other assets) and use it to pay off the money they owe to other customers who have deposited money with the failed bank. Any bank that accepts deposits has a moral responsibility to return the money deposited with them by the customers. And if they fail to do so, the government can interfere to help out the customers