1) Tailed beasts chakra within him - Naruto actually has seven of them:
. Now if Gaara transfered remains of Shukaku's chakra + Killer bee transfered remains of Gyuuki chakra into Naruto... then at least he would get pseudo Juubi mode and we know that Juubi has massive and very rapid instant regeneration and overhaxxed healing powers as Obito from being almost dead came to be alive and well after becoming ten tails host. It could have something with Gedo Mazou containing massive life force so it would keep him alive. - POWER UP and WAY TO SAVE A LIFE at the same time
2) Gedo Mazou arm - if Kakashi bring Gedo Mazou's arm:
ripped with his Kamui back and sealed into Naruto then at least it would give Naruto chance to be alive as Gedo Mazou is known for huge life force:
- Just WAY TO SAVE A LIFE.
3) Chakra of nine tails in Rikudou tools - It may be still possible for Nine tails chakra stolen by Kinkaku and Ginkaku be present inside jar as Madara just spit them so it may be foreshadowing:
- POWER UP and WAY TO SAVE A LIFE at the same time
4) Sage of six paths chakra's present in Naruto contained within tailed beasts chakra -
Sage of six paths as divine being inside human flesh could possibly even reivive Naruto and gives him power up. Nothing is impossible for this guy remember it - POWER UP and WAY TO SAVE A LIFE at the same time.
5) Nature energy saving Naruto via Sage mode in magic way or new stage 2 of Sage mode/enhanced Sage mode would allow him to cheat death or something - POWER UP and WAY TO SAVE A LIFE at the same time.
6) Obito will steal other half of kurama from Black Zetsu somehow and escape then transfer it to Naruto redeeming himself in the end and give hope for the world.