I don't quite understand how is a quantum computer any different from any other computer. Of course it is more powerful but that doesn't make it any better for hacking Bitcoin.
Blockchain simply can't be hacked, because what written in the chain, stays in the chain. You can't modify the past blocks. The only way to hack Bitcoin is to get someone's private key which means that you install virus to his computer or you get access some other way. But quantum computer doesn't help you with that.
I'm no expert on cryptography, but it is possible to break some of it with quantum computing. Current computer technology prohibits deriving a private key due to mathematical limitations. Quantum computing would allow someone to derive a private key using the Shor algorithm. There are ways that BTC could survive in the quantum age, but it will need some upgrading. I know there's been talk of adding Shor signatures and maybe POW will need to be changed someday, but I'm not worried about it right now.