Yes, unfortunately, Kurama passed away in the manga. This occurrence brought about a lot of changes and emotions for both the characters and the readers.
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.
It could develop as Naruto spends more time in the mental space where Kurama resides. They start to communicate better, understand each other's motives, and gradually form a deeper connection. This might involve Naruto learning about Kurama's pain and loneliness over the years, which makes Kurama more open to Naruto. As a result, their bond becomes stronger and more symbiotic, allowing them to share power more effectively and support each other in different situations.
In some fanfictions, Naruto becomes friends with Kurama through deep conversations. Naruto, being persistent, tries to understand Kurama's pain and anger. He shares his own experiences of being alone and ostracized. This mutual sharing of feelings gradually breaks down the barriers between them, leading to friendship.
Kurama might be the link that brings Naruto into Deathstroke's orbit. Since Kurama is such a powerful and unique entity in Naruto's world, his presence could be what makes Naruto aware of Deathstroke in the first place. For example, Kurama could sense some strange energy similar to Deathstroke's and draw Naruto's attention to it.