It would be possible to end it in the next 200+ chapters. Here me out:
-There are several arcs which are extremely small and short in length, yet they answer lots of questions and cover lots of material. A PERFECT example is Roguetown. It explained that people world-wide are suffering from the world govt., proved that there are a very small majority in the Navy who have clean hearts (Tashigi, Smoker), it let us know some villains may be returning with vengance (Buggy), AND it foreshadowed conections between Luffy, Roger, and the other 'D's and that they all may die the same way–laughing. And thats not even the only "tiny" arc that covered a crap-load of material: The same goes for Morgan (Zoro's past and Coby's departure), Romance Dawn, etc...
-All of the things we have left behind/unanswered (Shanks, Whitebeard, Blackbeard, Buggy, Dragon, True history, Raftel) are ALL connected in one way or another and it is most likely they will be explained/resolved within the same or close-connected story arc. Seriously, do you think theres is going to be an Alabasta 2.0 just about the relationship between Shanks and Whitebeard, and who Dragon is???
-All of the n00bs left behind probably aren't going to even scratch the surface. The only one significant so far is Teach (Blackbeard) and the shady Sichiukai. Even Buggy won't be that big, he's probably just gonna talk.
-The World govt. arc isn't finished yet. Whatever conflict the Straw-Hats may have with them is gonna be settled now, or a little later in a nicely wrapped package.
-The other mugiwara's don't need an entire Arlong arc to explain them and their back-stories. Remember how short Luffy, Zoro, and Usopp were?????? No arguements here.
So seriously people, it's not impossible this can be done in 200+ chapters or so. Don't get me wrong, I will be as dry as a desert crying when it's over, but do you want to be paying for your 18-year-old son's college tuition while still keeping up with this...? All good things...must eventually come to an end...