Kurama makes a comeback in the manga. The return is well-plotted and adds an interesting twist to the story. It also ties up some loose ends and brings new possibilities.
Kurama's death in the manga is final. There's no indication or plotline suggesting that Kurama comes back to life. The story moves forward without this happening.
Well, they could change a lot of things. Maybe Naruto would prevent some of the tragedies that happened in the past. He could stop the Nine - Tails attack on the village, which would completely change his own life and the lives of many in Konoha.
Well, Kurama might train Naruto by teaching him how to better control and access chakra. Since Kurama has a vast amount of chakra, it could show Naruto unique ways to harness and use it. For example, it could guide Naruto in creating more powerful and complex jutsu by using their combined chakra in a more efficient way.
He could meet his past self. It would be really interesting to see how he interacts with his younger, more naive self. He might try to give advice to his past self, like how to better control his power or avoid certain dangerous situations.