What will happen in case he suddenly re-appear after 1-2 years? He is the creator of Bitcoin, and we need to show our respect for him. And as long as these coins can't be spent, it can have a positive effect on the exchange rates. And I guess this is beneficial for all the users, with the exception of those traders who engage in short-selling.
The impact will be big, but real Satoshi if really exist won't harmed it's own creations, he will rather to keep being anonymous and holds those coins with him instead of showing up and create doubts that he will dumped all those coins that he's keeping and make a huge downfall.