I don't think satoshi nakamoto is dead , I only know he doesn't want to be famous ... and maybe one day he will come back online here in the forum and will post something.
We don't know anything for sure.
We can't even be sure that satoshi nakamoto represent just one person, not the organization, that he is Japanese or whatever...
But, we can be sure that he is genius, with brilliant ideas and that he started something really revolutionary.
BTC have some difficulties right now but I'm sure that soon we will see that price raise again.
Why he choose to remain Anonymous?
I think he don't like publicity and don't want to deal with the press or government.