And you know what would make that pardon null and void? If Obama turned out to not be Constitutionally eligible to be President — now, wouldn't that be an interesting tactic to take? Cutting through Obama's legacy/legitimacy to get at Crooked Hillary who would believe herself safe does have a nice ring to it.
It’s interesting as an intellectual exercise; But IMO the US Congress and more particularly the people do not have 1/500th of the attention span to manage such a complex unwinding process.
Suppose for the sake of brain twist we get to the kind of point you image in let’s say October-December. In one case, the elections have not yet been held, in the other, they have, and HRC wins. 0bama is discovered to have committed deep treason, so serious that even Dems look like they’ll vote to impeach him. What then?
He resigns, Biden steps in, pardons HRC, same result. We are hosed.