Wealth and value are not the same thing; wealth is an abundance of money and silver is not money (although at one time it was). Labor is not the promise that underlies money in this economy. If all currencies tanked, silver would be valuable on account of its relative scarcity and commercial/industrial usefulness. Whether it becomes money is another issue. Since all currencies won't tank, you'd better hope you have a means to facilitate your exchange of silver for money, or that your silver is in coins or sheets.