Sorry for leaving you alone (Rukia Hime) to these Itachi wanna be dead lovers, but i`m back now, and lets woop some asses
Itachi lives!

And he does a Killerbee 2
If Itachi did the same as Killerbee, he would either A: Stay out of Sasuke`s way and never show his face again, pretending to be dead like Madara did for many, many years.
Or
B: Only involves himself it the plot if things goes really bad.
Why Itachi appears you ask?
I can only see one of these following explainations for his comeback:
1: Seeing Sasuke get on such a dark and wrong path, he started doubting that what he gave Naruto would be enought, and decided to help him out.
2: Seeing/sensing that Donzou (is about to) reveal(ing) what Itachi said he would kill him for if he did
3: Seeing Madara brainwash Sasuke this much, and put his name in bad light, without telling the truth that he too was in on the massacre. So he will try to open the path for Naruto to be able to help Sasuke later.
Or 4: Itachi has a hidden agenda, whice is yet to be revealed

So in other words:
He`s either back to help Sasuke, to help donzou, to help them both(unlikely), to help Naruto and co. to help Sasuke and Naruto, or to help Donzou and Naruto