If no one mines bitcoins anymore, nobody can exchange them. Miners basically get a commission because they use their processing power to process transacrions between bitcoin wallets. So, if no one is mining anymore, which is unlikely for now, you will actually destroy the currency. Even if it is still worth something, you won't be able to exchange it, so it is like destroying it

Here are also some scenarios - although unlikely, still theoretically possible:

1-You break the cryptography behind the Proof of Work algorithm. It’s a mathematically sound approach, as it’s mathematically possible but just very, very, very hard.In simple terms: You can fake the complete chain if you manage to re-create a new chain which is longer than the real chain , which is completely sound to all the mathematical constraints for blocks and transactions, in the time it takes the other miners to create the next valid block. Potentially possible, for example if you build a quantom computer in your garage and work out an algorithm which is able to do that.

2-A massive restriction on global scale: Governments all over the world restrict the contact points with regular money and make it very, very hard to exchange Bitcoins. Which would make it useless for transactions outside the network.