For as long as Bitcoin has existed, it has always been a possibility. Some like to think Satoshi purposefully threw away the keys to his multiple wallets because he knew how risky keeping that much btc was. Personally, I believe that he still has access to the wallets and hasn't touched them for three main reasons. Firstly, he knows that people would notice if he sold his bitcoins, which has the potential to destroy faith in the whole project. Secondly, he's aware of the fact that selling so many bitcoins would most definitely disrupt the market. Thirdly, as the visionary behind blockchains, he has an unshakable faith in Bitcoin and is certain it will succeed in the long term.
Whoever this Nakamoto really is...he must be a man of his words and somebody who has no desire to well-known and be officially recognized as the man who started everything crypto. And I have a great respect for what he did and his eventual decision not to interfere in any way on Bitcoin.
Of course, it is his right if he wants to dispose of his hoard of Bitcoin but I don't think he will do it in a way that disrupt the whole thing...I mean he can dispose it slowly making it noticeable.