Even if Satoshi presents his privatekeys, signs messages, shows his passwords, e-mail account accesses... it could be someone else who has all these privatekeys, passwords, accesses now.
Not true. A real investigator would be able to piece together other evidence which could prove or disprove that person's assertion that he's Satoshi. I have no doubt that there could be proof enough to satisfy most people, tho I'm sure there would be conspiracy theories in any case. It's *not* impossible.
But if satoshi sign message in her bitcoin wallet
I'm fairly certain that Satoshi isn't a woman. That would be quite a story if that were the case, but I'm thinking if Satoshi is really a single person, he's a male.