Why do people keep assuming that Kakashi is done? If Kishimoto decides to kill him, I will take back what I am about to say:
-Obito is not greater than Itachi, Nagato, Naruto, Madara, the 4 Hokages or Sasuke. His Kamui is what makes him good. It has been seen a few times that smart ninja can see through Obito's deception. For example, the way Minato analyzed Obito's technique and defeated him. Or when Kakashi went inside of Obito's Kamui dimension and attacked him from the inside while Naruto attacked him from the outside (basically putting him on the same playing field as everyone else). In terms of techiques and abilities, I believe those I listed above are better than Obito overall. You can't disagree with me over that.
-If Obito could rid of Madara with Kamui, he would have done it already.
-Kakashi and Obito are on the same level more or less. Obito has Rinnegan and Senju DNA... big deal. It seems that all he knew how to do with his Rinnegan was create the Jinchuuriki paths. His Rinnegan hasn't done anything else for him in this battle. The Senju DNA is only on his right side. His left side is still vulnerable and he can be killed if fatally hit on his left side (the hole in the heart thing was just a genjutsu, he was using it as a metaphor for the fact that he is now "heartless). Since Obito isn't using his Rinnegan... he and Kakashi are about the same. Kakashi is a master of many jutsu's and techniques. Obito has wood jutsu thanks to Senju DNA. They both have Kamui. Since they are both in the Kamui dimension, the playing field is now even.
-I am not saying that Kakashi can't lose, because he can. You have to put Kakashi in Naruto's shoes now. Naruto didn't want to kill Sasuke during the course of part 2... he wanted to change him and bring him back to the village as a friend.
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After they clashed a second time (when Sasuke was crazy and unreasonable), Naruto made the decision to kill him in order to save his friend.
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Kakashi didn't understand Naruto's feelings at first
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-But now he does. Kakashi doesn't want to kill Obito, he wants Obito to return to the light and become his old self again.
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Just like Naruto, Kakashi just had that brief talk with his old friend and now understands his feelings and sees he cannot return to the good ol' days.
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-Just like Naruto, Kakashi may decide that the best way to help his friend is by killing him. That is why I think Kakashi will go back to being a badass soon enough.