Ghost was NEVER his. It simply was meant to help him against Natsume since Ghost-types were best for Psychic-types. Proof that it isn't his is that we never see it in the openings along with any Pokemon that Satoshi's captured before (Spear doesn't count since he barely even had it for a whole episode, same goes for Ratta).
Pidgeot will come back when the writers finally decide to do so. They haven't forgotten about it as we've seen all of his older ones in the Japanese openings.