If you have a large stash of cash and something horrible happens to it -- like it's seriously damaged in a fire or a flood -- is there any way to get it replaced? Possibly. "The Bureau of Engraving and Printing redeems partially destroyed or badly damaged currency as a free public service." The guidelines on what qualifies as "mutilated currency" and a link to the instructions for submitting a claim can be found on this page:
Once you get your replacement currency, you may want to reconsider the wisdom of keeping it in your mattress.