Madara is kind of a spoiler of what is to come in the battle between Sasuke and Naruto. Super Susanoo is the only way that Sasuke can complete against Naruto at this point. In order for him to even realize that his own Susanoo is so pathetic, he needs to see Madara's version. This leads me to believe that somehow Madara will avoid fading away, Susanoo will not disappear with Madara, or Itachi is about to put Sasuke under Tsukuyomi in order to have a final conversation with him. Regardless, if we don't see the stabilized Susanoo in action now, we will probably see it later when Sasuke does the same thing when fighting Naruto.