Board Thread:Naruto: The Last Discussion/@comment-7606564-20150323235325/@comment-5233512-20150328120657

I believe he does retain some of the Six Paths Chakra, but that was confirmed in the "Naruto Hiden" novels. ("Shikamaru Hiden" if I am not mistaken.)

Also, you are inferring that Madara is the strongest ninja in existence, right? Then that way, Naruto and Sasuke would be tied as the second-strongest ninja in existence. Of course, this would be under the assumption that the two sons of the Sage of the Six Paths, Asura and Indra, do not count as ninjas.

However, I believe that by the end of the manga, either Naruto or Sasuke can defeat Madara with their newly gained powers. They have, in a sense, become the new gods of the ninja world and should be considered to be tied for the first-place as the strongest ninja in existence.