There are many reasons FP (in its previous form) may not return. However the park pass system is not an obstacle that prevents FP+ from functioning.
Yes, yes it is. If you take a building that houses one show, and put a new show into the building. And you want to keep the new show. It's not that easy to bring back the old show... you would need to construct a new building for it.
Park pass code was not "new" -- It is an adaption of the FP+ code. You'd need to go back to the drawing board if you wanted the code to accommodate park pass AND fastpass.