FBI would've nailed Hank regardless
Think about it - they have the location of the plane, that they knew had 4.4 million in it, but the cash has mysteriously shrunk to $500,000. Where did the other 3.9 go? Then they realise the sheriff took this local guy out to the reserve because he was linked to the money because had reported hearing a plane, the guy ends up being the survivor of a shootout that left 3 dead. Then they realise that this same local guy just weeks earlier was a survivor of a double murder situation at one of his friend's houses. It is never discussed, but in both of those situations there would be a crime scene analysis in which there would be flaws in Hank's story - for eg. how exactly did Hank shoot the kidnapper in the face, how did he get so close if the man was armed, at Lou's house there would be shells and blood splatter in locations that don't match his version of events, which already had discrepancies with the other witness (Jacob) etc etc
I think they would very quickly put together that Hank is in it up to his ears and they would simply search his property where they would find a gym bag containing the missing 3.9 million. Then they would do him for 5 murders!