That alone would not be enough for Bitcoin to be replaced by another cryptocurrency, because Bitcoin could receive a quantum cryptography in its code, to protect the network against possible attacks.
There are already solutions available for this, and I think the Litecoin developers are considering implementing this kind of protection.

From the last time I saw them discussing this: https://www.reddit.com/r/litecoin/comments/53xrnh/do_we_need_to_make_litecoin_quantum_resistant/