Firstly sha256 is not an encryption algorithm, its a hash.
Bitcoin mining is done with sha256d (sha256(sha256(data))). There is no reason to believe that quantum computers are more efficient at calculting sha256d than ASICs. Lets just assume they are 100 times better anyway. What would happen? We would have a difficulty increase. For a short time blocks would be found quicker, afterwards everything would be back to normal. This is even true should QC be 2128 times faster, but it might still be a good idea to jump to a different hash function if the difficulty becomes to high to grow further. In this case it would require new specialized hardware. I dont think we will ever go back to GPUs.
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It seems to me like every 2-3 months someone comes up with this topic; it's starting to look suspicious if you ask me. I'm not even sure why the forum allows this because technically they are duplicates and there are many of these "quantum is dangerous, and I'm scary threads". It is becoming tiring saying the same thing over and over again. Bitcoin mining is done with sha256d (sha256(sha256(data))). There is no reason to believe that quantum computers are more efficient at calculting sha256d than ASICs. Lets just assume they are 100 times better anyway. What would happen? We would have a difficulty increase. For a short time blocks would be found quicker, afterwards everything would be back to normal. This is even true should QC be 2128 times faster, but it might still be a good idea to jump to a different hash function if the difficulty becomes to high to grow further. In this case it would require new specialized hardware. I dont think we will ever go back to GPUs.
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There most certainly is.
Not before either: 1) You die; 2) Bitcoin becomes obsolete. I think you misunderstand. When I say 'cracked' I do NOT mean computers brute forcing their way through like you describe. I mean some maths genius comes up with a shortcut so my home pc could get a private key from a public key.
This doesn't happen overnight or else nobody would even consider using any of these algorithms. The chances of a meteor wiping everyone out are probably higher than the chances of a "genius" destroying SHA256 in the next 50 years. Should you be scared and panic? No. Focus on what is important, not on what might be. Update:
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I didn't really mean forbid in general; there are threads about quantum related things that are only a few months ago and one could easily just ask their questions there and the discussion would become active again. However, I do understand your point as well and I do agree with you. I didn't want to write an additional post since this might be a bit off-topic to the actual thread so hopefully you will notice the update. 
.... Do not lose too much sleep over this. 
