I don't think Satoshi will cash in all of those Bitcoins. Even if he cashed in some of them, the price of Bitcoin would probably drop because people would expect all of the coin to go back into circulation.
You never know when and what the real Satoshi will be thinking,if he really wants those coins he have saved at the beginning he will move now or at a later time and no one can stop him from doing that. The price of bitcoin will crash only if he plans on dumping all of his coins which is highly unlikely other than that if the coins moves we might see a minor correction because of fear that he might dump everything.
Its just your thought that bitcoin has been holded by the Satoshi now moved to other hands. Actually, this will not be truth I think because the He is one speculates first bitcoin will be reach to 10000$ for one bitcoin. As of now it doesn't happened. May be, Its happened he come out to the real world and say the truth.
It wont happen since Satoshi wouldnt really come out no matter what happens since he do know what will be the things might happen to him.We dont know or no one could really justify if he does hold huge amounts of bitcoin on hiw own pocket since hes the owner or creator of bitcoin.If he does hold that amount then possibly he can surpass bill gates specially when the price skyrocket on to high point.