If Satoshi is alive, quantum computers would be the least of his concerns.
Perhaps he hasn't moved his bitcoins because he doesn't need them, or maybe he wants to protect his privacy.
His only options would be to try using mixers, but that would lead to a pursuit to uncover his identity.
The most daring option would be to gather all his bitcoins and distribute them to a batch of thousands of active individuals/addresses on the internet, sending BTC Strategically to each active user's addrs, with some of them being his own wallets. In this way, he could have millions to use without risking revealing his identity. It would be a historic move, although it would certainly influence the price if he doesn't do it in periods of time to avoid drastically influencing the market.
There is also a possibility that if Satoshi is alive, he has a separate Bitcoin holdings that warrant him of a luxurious life while not touching the one known by the public. Satoshi is a smart person we all see that, if he planned all this disappearance and not touching his millions of Bitcoin sitting in an address known by the public, he probably have made another Bitcoin address that is not linked with the one known by the publice and holds a good amount of BTC for personal use.
Btw, I believe quantum computer is overhyped, I do not think it would be that destructive to securities when it is implemented. Remember as technology develop, digital security also develop. There is a huge chance that anti-quantum computer encryption will be created or developed even before quantum computer starts breaking digital securities.
