Ive explained this. Itachi wont stop the war. Oro is going to use Edo Tensei to revive Itachi, and go find Minato. Then, the two of them will fuse using the Potara earings (they cant do the dance with one arm...), form Minachi, the savior of the universe, and defeat every foe there is.
Madara survived due to pnj that much is obvious, otherwise If Itachi hadn't deactivated ET he would have solo'd Madara no diff. and would have one shot Obito and Naruto both for being little paralleling *****es.
Kishi couldn't allow Itachi to meet and solo them it would have ended the manga too soon which would mean less money for kishi.