Well, it could be that Naruto and Kushina reunite in a sort of spiritual realm. Kushina might teach Naruto some new jutsu that only she knew. And they could bond over stories of the Uzumaki clan, which Naruto doesn't know much about. Also, Kushina might give Naruto some advice on how to handle his relationships better, especially with Hinata.
In this fanfiction, Naruto might finally get the motherly love he always craved. Kushina could share her unfulfilled dreams for Naruto, like seeing him grow up without the pain of being an orphan. They would probably have an emotional conversation about Naruto's father too.