Before we make assumptions and predictions, I think we must know first about quantum computers. Actually, I have read about this new technology before and now that this topic has been opened, I am thankful that I have knowledge regarding it. Quantum computing is invented not to destroy blockchains or affect the safety of cryptocurrencies. It was invented because of the need to perform fast and very complex solutions and equations that a super computer cannot do. The world is constantly developing day by day - with the aid of technology. I think it is easy to predict the next invention but its function on the other hand is not easy to know. Scientists and inventors of today and the future generation is highly capable. Besides, what would be the reason for them to destroy blockchain? Satoshi might be able to assume the occurrence of quantum computing but its effect on bitcoins as you were saying (which is really none) is not.