WARNING: The following contains spoilers for Chapter #55, “Legacy,” of Boruto: Naruto Next Generations by Masashi Kishimoto, Mikio Ikemoto, Mari Morimoto and Snir Aharon, now available in English from Viz Media.
For some time, it seemed as if the Boruto manga was going to kill off Naruto. When he went into the Baryon Mode against Isshiki Ōtsutsuki, Kurama said it'd drain him and leave him dead, stoking these flames even more, and when fans saw Sasuke worried about him being unresponsive after the victory, it looked like time was nigh.
Luckily, Chapter #55 doesn't murder the Hokage, but it does kill off Kurama, his closest ally. This all happens thanks to a little white lie told in the heat of battle. It's a heartbreaking moment for Naruto fans who've grown attached to the Nine Tails, seeing the Demon Fox go from Naruto's enemy to more like a sibling and eventually like a parent.
Naruto's taken to the astral plane he often shares with the Tailed Beast, and Kurama admits it's time to say goodbye. However, he informs Naruto he's the one who'll be going, exposing the lie. He admits that had he told Naruto that Baryon Mode would kill him, Naruto wouldn't have done it. By saying it'd kill Naruto, though, he knew the Konoha legend would be self-sacrificing, so he decided to dupe his host. It's a smart move to use his vessel like this one more time, saving the free world again.
It's really hard for Naruto to say goodbye to someone who looked after him for so long. He lost Jiraiya and got over that, but as he begs Kurama to stay, one has to wonder about the mental impact of him losing another loved one. Then, there's the physical impact -- usually, if a beast is extracted from a host, that person dies, but in Kurama's case, his chakra is simply spent and disappearing. It's assumed Naruto will be safe and sound, but the after-effects remain to be seen.
When Kurama was corrupted decades ago, he killed Naruto's parents and got sealed in the child, so his story is definitely a bittersweet one -- one filled with redemption and a tragic conclusion. Not only did Naruto set an example and forgive the beast, but Kurama forgave the village and vowed to protect them with or without Naruto.
Now, the Hokage will have to soldier on without his best friend, someone who was like an uncle to Boruto and Himawari as well. Naruto will also have to fortify if he intends on stopping future threats like Isshiki. Perhaps someday he can use science, new jutsu techniques, ancient scrolls or chakra mysticism to reconnect with his buddy, but for now, Kurama is gone. As Kurama dissipates, the fox warns him to be safe, or else their reunion will be in the afterlife.