I have not read the comments, not sure if anyone pointed this out, but the truth is . if quantum computers are going to be a threat to anything then the last of anybody's concern would be bitcoin. the whole world will be at stake, starting from banks to secret intelligence
but really QC is not as scary as it seems.
as far as bitcoin goes, i do not see that MUCH of a threat coming form QC.
1- For the mining part, indeed QC based miner could out perform a non-QC miner but i am willing to bet the horse that the cost will be very high , by the time the production of a proper QC based miner which can beat a non-qc miner , all BTCs would have been mined and we all are going to be dead anyway. and regardless of my theory , there is no way that QC miners will mine all the remaining BTC in no time as many people think (thanks to the difficulty)
2-The strength of QC relies on the ability of cracking a private key from a public key, the great security measure in BTC is that the public key goes through 2 hash functions (RIPEMD-160 and Sha256 ) which are not very vulnerable to QC
[1]. of course this means you will need to use a new address for every transaction as your public key would be revealed after using it which could be inconvenient but this threat excist as of today that's why most people use automatic key exchange.
[1] QC or even existing computing can break both hash functions, but if you have the computing power to do so then it would be more profitable for you to mine bitcoin and be ahead of everyone else.
also by the time this treat comes, we would have had more security measures.
so no bitcoin can't die because of qc, it can die for other reasons tho