it was obvious from the beginning that Naruto will be the one to TNJ Obito (Obito will die as a good guy, will do one final act to redeem himself).
as for Jiraiya returning .............. maybe Orochimaru had a sample (maybe blood) from Jiraiya before he died (an old sample) BUT, i doubt it.
i always used to think that his return might ruin the story/his glorious death BUT, everyone is coming back/the war is messy so ............... why not.