why he disappear ? is he dead ? i don't find any reason that's why he disappear...if he comes future he will be ask to proof himself it would be awesome if he back to this forum with a topic like "time is over for hiding".
Nobody knows for sure. "Satoshi" disappeared around the time now-Lead Gavin gave a presentation for the CIA (or FBI - I don't remember, anymore) a few years ago. Whether or not that's a coincidence is unknown. He may be alive or dead. He may be named Nick, Dorian, Ralph, or Tariiq, among millions of other letter combinations, though it's suspected he was White, distant second possibility being Asian - but he wrote in UK English, so we can probably rule out American origins (unless he was just that damn sneaky!).
If he came back, it's unlikely he'd be fully believed to be the original "Satoshi," even if coins moved or "he" signed using his last known PGP key. If coins moved today, I'd guess the majority would assume Satoshi's identity and keys have been fully compromised and a giant pile of coins are about to be dumped, which has some interesting possibilities (does an exchange have the right to block coins from being sold if they suspect the seller of "Satoshi's coins" is not the original "Satoshi"?).