If you are in possession of classified documents and not authorized to have them, you are in violation of US law and subject to prosecution regardless of your nationality. There were classified documents on Hillary’s private server.
He would only get a pardon just from offenses against the U.S. government. But there is still that rape charge in Sweden...altho’ that case may soon phase out via statute of limitations running. The guy has been holed up in the Ecuadorean Embassy in London for 6 long years...he’s already lost his freedom for 6 years altho’ more comfortably than being imprisoned...and possibly those 6 years are more than he would have served if prosecuted initially (however, he could have had a fatal “accident” in prison). If he can return to Australia, he’ll still have to be cautious, as too many people who are on the receiving end of his exposures are out for his blood IMO.