I've revisited Midgar once when I whupped up the big red robot thingy and Hojo. However, when I later lande the airship outside of Midgar and walk to it, I end up outside the big gate where you got out the first time (on disk 1, I mean). A man is standing there and says he's missing his entrance card or something, and that he think he lost it on "the excavation tour". I've dug around over at the excavation place, but I can't seem to find it. Is it possible to return into Midgar?