Hashirama and Tobirama were essentially brought back to life just to tell their story. The reason Kishi will write it this way is simple: A 3 way fight between Team Kage, Taka and Orochimaru would take too long to resolve. He needs to wrap up the war soon, and a prolonged fight won't do that. Instead I think we will see EMS Sasuke fodderize Hashirama. Fanboys will of course be pissed at this, but there are reasons:
1) Hashirama and Tobirama no longer have relevance to the plot. Madara is Naruto/Alliance's foe. As a mover of plot, Sasuke will draw the curtain on them.
2) EMS Sasuke has yet to show his hand. Against Kabuto Itachi told him to take it easy. In other words, Kabuto was weaker than Sasuke even with Oro DNA. By association, Orochimaru with arm chakra is (duh) weaker than EMS Sasuke. Sasuke gains status by showing he has also "surpassed the Kage" as Naruto has.
3) Sasuke is and always has been about revenge. Hashirama's explanation will help Sasuke decide that his revenge against Konoha is justified: The Will of Fire is a hypocritical oath that destroyed his entire clan by allowing Madara to live (and thus Obito to survive) This will serve to show Sasuke that Naruto's way of thinking will only create more conflict as Hashirama did. In other words, Sasuke will decide that the only way for him to fulfill Itachi's wishes is to follow his brother's path.
The end of the path of darkness is pretty clear, guys. Revenge swallows a person, and consumes them in absolute negativity. It's path is self-destruction. Sasuke will decide to follow this through to the end as Itachi did, and to sacrifice his life so that Naruto can fulfill his destiny. Sasuke, like Madara, will be unable to accept that his brother chose to suffer. He will see himself and Itachi as victims of a long-standing feud that was the result of Hashirama's foolish, naive idealism and the hypocrisy of allowing Madara to live.
Basically, I call it like this. Flashback ends. Orochimaru makes his move to take Sasuke, but is stopped by genjutsu. Hashi intervenes and moves to stop Orochimaru. He is shocked to see the Totsuka Blade piercing him from behind. Sasuke kills Hashirama, at which point Tobirama intervenes and is also killed by Sasuke. They warn Sasuke as they are dying to not repeat the mistakes of the past. Sasuke resolves that if his clan is a mistake, then he will erase the Senju moralism from the world once and for all.
Orochimaru is made a mind slave. Minato is rewritten entirely and commanded to kill Naruto. Sasuke uses Hiruzen to absolutely destroy Konoha. Edo Hiruzen is stopped by Konohomaru, but the rest of Konoha is entirely annihilated. Naruto and crew beat Madara, but return to find their home completely eviscerated by Sasuke. Standing in the burning remnants of Konoha, Sasuke will motion to Konohomaru's lifeless body. The alliance moves forward against Sasuke, but are blocked by the Edo Uchiha clan, Minato and Hiruzen. Naruto demands an explanation but is shocked when Sasuke fires Chidori Senbon and kills Sakura mercilessly before his eyes. The final arc begins.
1) Hashirama and Tobirama no longer have relevance to the plot. Madara is Naruto/Alliance's foe. As a mover of plot, Sasuke will draw the curtain on them.
2) EMS Sasuke has yet to show his hand. Against Kabuto Itachi told him to take it easy. In other words, Kabuto was weaker than Sasuke even with Oro DNA. By association, Orochimaru with arm chakra is (duh) weaker than EMS Sasuke. Sasuke gains status by showing he has also "surpassed the Kage" as Naruto has.
3) Sasuke is and always has been about revenge. Hashirama's explanation will help Sasuke decide that his revenge against Konoha is justified: The Will of Fire is a hypocritical oath that destroyed his entire clan by allowing Madara to live (and thus Obito to survive) This will serve to show Sasuke that Naruto's way of thinking will only create more conflict as Hashirama did. In other words, Sasuke will decide that the only way for him to fulfill Itachi's wishes is to follow his brother's path.
The end of the path of darkness is pretty clear, guys. Revenge swallows a person, and consumes them in absolute negativity. It's path is self-destruction. Sasuke will decide to follow this through to the end as Itachi did, and to sacrifice his life so that Naruto can fulfill his destiny. Sasuke, like Madara, will be unable to accept that his brother chose to suffer. He will see himself and Itachi as victims of a long-standing feud that was the result of Hashirama's foolish, naive idealism and the hypocrisy of allowing Madara to live.
Basically, I call it like this. Flashback ends. Orochimaru makes his move to take Sasuke, but is stopped by genjutsu. Hashi intervenes and moves to stop Orochimaru. He is shocked to see the Totsuka Blade piercing him from behind. Sasuke kills Hashirama, at which point Tobirama intervenes and is also killed by Sasuke. They warn Sasuke as they are dying to not repeat the mistakes of the past. Sasuke resolves that if his clan is a mistake, then he will erase the Senju moralism from the world once and for all.
Orochimaru is made a mind slave. Minato is rewritten entirely and commanded to kill Naruto. Sasuke uses Hiruzen to absolutely destroy Konoha. Edo Hiruzen is stopped by Konohomaru, but the rest of Konoha is entirely annihilated. Naruto and crew beat Madara, but return to find their home completely eviscerated by Sasuke. Standing in the burning remnants of Konoha, Sasuke will motion to Konohomaru's lifeless body. The alliance moves forward against Sasuke, but are blocked by the Edo Uchiha clan, Minato and Hiruzen. Naruto demands an explanation but is shocked when Sasuke fires Chidori Senbon and kills Sakura mercilessly before his eyes. The final arc begins.