In this situation, Satoshi could bring down the price if they want to, but I don't think that it would be completely devastating and irreparable. It could be an event leading to years of stagnation, but I believe Bitcoin would recover anyway. I also believe that if Satoshi decided to dump everything, they would do it via OTC deals because of the huge sums involved because dumping such sums on exchanges would be way harder and take more time and effort. In that case, the price wouldn't even change much because such deals aren't done on exchanges and thus the general demand and supply for BTC on exchanges remains the same. The only thing that would follow is some FUD, but that probably wouldn't have lasting effects on the price at all.
No matter what Satoshi does with his/her/their Bitcoin, the community is big enough to make it rise again to its former glory. There are many whales, institutional investors, and average traders on the market constantly buying/selling Bitcoin. If there's a huge dump, prices will quickly rebound until the original threshold is reached. I doubt Satoshi would move his/her/their Bitcoin holdings since it would expose his/her/their identity to the public. Authorities will quickly trace the transaction with the hopes of discovering who Satoshi really is.
That's why for the sake of Bitcoin and the entire crypto/Blockchain space, it's best for Satoshi to remain "dormant" for the foreseeable future. What will happen with Satoshi's stash of Bitcoin in the long run is a mystery. As long as there's a community backing Bitcoin, there should be nothing to worry about. Just my thoughts