 Actually, I did an essay on this. If you look at this, it says it was titled cryptography after the alien's land. My name, and you'll find it. The short answer is quantum cryptography is not the end of cryptography. For symmetric keys, you double the key length. That's easy, but we already have a process for quantum-resistant public key algorithms. Even if they fall, you're not losing security. This has an entire key infrastructure without public key at all, and works just fine. So it'll be different. It won't be a disaster. We are well ahead of the technology cryptography than there is in quantum. So short answer is don't worry too much. There's a lot of other things to worry about first.