But they Sage didn't say anything about them being permanent either. Its obvious that there based on the powers of Indra and Ashura, if they finally are able to end the conflict that means bye bye to there reincarnated powers.
And I feel its more likely to lose them because it would go against how Naruto is suppose to secure peace, it won't the message of secure peace because of love, it will be you better secure peace because Naruto is the most powerful ninja in the world.
If the sage prophecy is true, Naruto should be leading in times of peace.
I don't think the Sage split the power, he just awakened the powers already existing within Naruto and Sasuke, Sage awakened Ashura power and Naruto gained new sage senjutsu, and sage awakened indra power and Sasuke gained the sharigan/rinnegan thing.
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It was never said the reincarnation chakra leaves them once its resolved, its a life long thing, it wasn't their conflict that caused them to be reincarnated it was their powerful chakra.
And how does having great power go against his goal of peace, he wants to protect his friends and that requires great power, or is Naruto going to protect them by hugging the people who try to kill them.
Just because the wars stop doesn't mean the world will be a perfect place without any problems or conflict, there are always going to be problems.
Naruto's goal was to become Hokage and become the greatest of all and surpass the previous ones, now he has done that (power wise).
Also the powers didn't come from reincarnation, the Sage gave his powers to them, he clearly said he was giving them half his power.
Indra didn't have the Rinnegan, he had a Sharingan.