There are many different ways that ruling could go, some of which could decide the google vs oracle by itself while not universally ruling on wether APIs can be copyrighted.
But the way it is likely to go is to affirm the CAFC's copyright rulings, which will become precedent nationwide, if the justices' lines of questioning are any indication. To do otherwise would be to completely undermine the copyrightability of software, if not copyright in general.