They can be used to power another decentralized consensus system. Currency is only one application being used on the bitcoin network. If bitcoin dies for whatev

They can be used to power another decentralized consensus system. Currency is only one application being used on the bitcoin network. If bitcoin dies for whatever reason (political or technical) the hashing power could still be used to secure and build another decentralized consensus network that could have many other functions other than being a currency: such as ways to send stocks, bonds, smart property and so on... in an entirely decentralized manner.