I have been reading One Piece since 2006. At the end, most likely I would read it by myself and cry silently for several minutes, be glad to meet with Straw Hats and live their story to end.
For the later hours I would be in shock as there wont be a new chapter.
For the later weeks I would try to by the Shonen Jump issue in which last chapter is released. I would buy lots of One Piece goods and put it every corner of my home which will force me to remember the holy story of Straw Hats.