>>37448887My headcanon for the longest time was that Red died inbetween RBY and GSC. He conquered every trainer, gym leader, and captured every Pokemon. When he was exploring Mt. Silver, he got caught in an accident, whether an avalanche, injury, or just merely froze to death. Nobody was able to find his body because the mountain was so dangerous, and as such became restless. You find his ghost in GSC/HGSS, and was defeated. Satisfied that there's another trainer that can carry the legacy of being the very best, he departed into the afterlife, which is why he vanishes without a trace.
Too bad BW2 and Gen 7 pretty much shattered that theory. Now I don't know what the fuck he's doing up there.