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And Sasuke's way of ending the of Indra and Ashura is becoming immortal or taking Indra's place or something(according to viz), Hagoromo couldn't stop it so there is no other way.
So Sasuke must become immortal to stop the reincarnation of Indra and protect the Shinobi world and continue his research in the different dimensions and planets which takes a long time.
What do you think? will he become immortal like Orochimaru?