2020 is a red herring as Fox own distribution for "Star Wars" in perpetuity anyway, so the companies are going to have to negotiate at some point.
It'll get done - Fox want the money, and Disney want the money and fan goodwill.
I'm quite sure Disney has seen the collective groans at past SE releases, documentaries like "People v GL", and booing of Greedo shooting first at screenings, etc.
They don't want that - and the primary cause of that is now happily enjoying his retirement.