Improvement of Bitcoin source code is one of good reasons, I agree.

However, it does not mean satoshi has to appear in public in order to contribute to Bitcoin source code. satoshi can make such contribution in a shadow and it's thanks to a real decentralization of Bitcoin, isn't it?

satoshi decided to leave our community but he did realize that there are different ways to contribute to Bitcoin.

Sum up, no good reasons to appear again in public.