I doubt any hokages will actually fight...because if they do, it'll be an easy win as enemy isnt that strong, its an equal match-up even without the hokages.....
I predict Hashirama will give up his life for tsunade, & minato is there for kyubi's other half chakra....he'll be dead again due to another plot no jutsu, like kyubi's half chakra can be obtained only if someone does the shiki-fujin summoning again....hiruzen & oruchimaru fight can also be nice.....just dont know what'll happen to tobirama....probably, he can go to the war,& we'll have naruto vs sasuke, madara vs tobirama & tobi vs kakashi....& eventually, tsunade(after gaining strength from hashirama) will come to rescue tobirama & they both defeat madara...