If all the bitcoin Satoshi owned were sold on the market, the market would instantly turn into a bear market and that would be much worse than the whale could do.
Don't be surprised it might not go as you think. Those coins are already tagged that of Satoshi and I'm very positive there is already been system put in place to keep track of them. We have those or group of whales who'll be willing to take all out if his wallet if he ever think of selling them but of course that's just our imagination because nobody intentional want to lose money as Satoshi knowing fully well the capacity of bitcoin disrupting the economy won't want to let go of his bags.
In a situation where your scenario turns out to become the case then as always we'll still recover from the bear market. That's not new to us as the market has constantly been doing that in the period if the last 10years. In conclusion, Bitcoin is now bigger than Satoshi Nakamoto.