Minato can use most of Tobirama's techniques or seals, so I reckon he will give Naruto his soul somehow. All hope is not lost because Sakura's hand is still in Naruto's heart still keeping the heart going, so someone probably Tsunade could give her life to Naruto and say "He reminds me of them, and I won't loose him like I lost those two in the past, you must achieve your dream as my successor… when he wakes up, tell him that he's the 6th Hokage!!!" Then she gives her life like lady Chiyo did for Gaara after they fought off akatsuki