Maybe, Itachi knew that Sasuke would never kill Naruto (Itachi's forecast is unparalleled) because Sasuke would never do what Itachi did i.e. follow his footsteps, because of the hate against him. That's why he confidently told Sasuke to kill Naruto for the sole purpose of acquainting him about the MS activation process.
True. But what then?
I agree. Sasuke wouldn't be a Zetsu because he can resist IT, but he most probably wouldn't be alive by then.
Sure. But he probably knew that Sasuke wouldn't kill Naruto. He planned about his death from Sasuke's hand long ago which also contained Sasuke's MS activation plan (by Itachi's own death).
Not necessarily. The plot has no interest in Sasuke vs Pain fight. But Sasuke would definitely get killed sooner or later, maybe in the war against JJ Obito or JJ Madara (2 Rinnegan).
If plot supports him i.e. progresses in a way favorable for Sasuke, then yes, because Sasuke has counters to most of Pain's powers. But if it is a pure power match up, then Sasuke loses, because a CT will end Sasuke's life.
Why would Pain even fight Sasuke? What interest will he have in that? None. There is no way Sasuke is dying prior to the war because he won't be a target of any powerful opponent.
BTW, EMS Sasuke can defeat Pain. But yeah, Sasuke would die sooner or later, against JJ Obito, if lucky then against Madara, or if very lucky, then against Kaguya definitely.
It took plot only for SM Naruto to fight/keep up with Pain, the 9 Tails didn't need plot support. MS Sasuke with plot can defeat Pain.