[MayeulC]

In theory, you may be able to ask the LLM about the person's life, as if it was the person, but you won't get more facts out than you provide as input. It may still make up credible info.

Regarding your last question, it wil lack an enormous ammount of data that make up a person's experience. Moreover, talking to sound like <X> isn't the same as thinking like <X>.

It reminds me of the later part of the book Accelerando, where synthetic personalities made up from historical records (could be anyone from Cleopatra to Newton) keep being reincarnated in a near, post-singularity future. They are handed out an FAQ that tries to bring them up-to-date on the current state of affairs.