The case would still go to the Supreme Court eventually; SCOTUS is relevant here as the court of final appeal for all federal cases.
The facts of the case, as well as Assange's personal obnoxiousness, would probably not be the best choice of a test case if you're looking to protect whistleblowers. Ellsberg is a much more sympathetic defendant.
I was thinking more of Assange's options for not being confined for the rest of his life. Honestly I think the odds are low of the UK government releasing him/declining the extradition, and less than even of the US government dropping the charges. He has already been practically imprisoned for years, plus actual imprisonment recently. Leveraging the threat of a Supreme Court fight against a face-saving US govt. approved light sentence might be a valid strategy at this point.
The facts of the case, as well as Assange's personal obnoxiousness, would probably not be the best choice of a test case if you're looking to protect whistleblowers. Ellsberg is a much more sympathetic defendant.