From the very start, he was already anonymous, and the fact that we've reached this level already shows the trust of the investors. I might even be concerned if he appeared, as it could change everything about Bitcoin being the best asset - who knows, it might be replaced by another asset.
How would Bitcoin change if he returned? I really don't think he can change anything about bitcoin because he is basically the creator of bitcoin but to make bitcoin more perfect he gave control of bitcoin to the community. That means bitcoin is independent of any individual, no one can control it, not even its creator. Any change to bitcoin requires the consensus of all the developers and he is just one of them.
There’s a reason why he kept himself anonymous, and one big reason is to stay safe with all the wealth he holds. If you were someone holding close to 1 million Bitcoins, would you make yourself public or keep your current status?
I think he decided to remain anonymous for his own safety rather than to protect his assets. Because at the time he disappeared, the value of those 1 million bitcoins wasn't that great and he had no idea that bitcoin would become as great as it is today.