Naruto’s latest transformation known as Baryon Mode, has allowed the Seventh Hokage to access a new level of power that was previously though to be impossible. However, similar to the other “impossible power” that Might Guy wields, The Eight Inner Gates, Baryon Mode strips the life from its user.
However, unlike the Eight Inner Gates, Baryon Mode doesn’t result in a certain death, it instead drains the life from the user as they slowly run-out of Chakra. Naruto was able to reduce the negative side-affects to his and Kurama’s body by absorbing Isshiki’s life-force in battle and giving him the bulk of the draining but that didn’t solve everything.
It did help Naruto and Kurama to take Isshiki’s Chakra but it didn’t mean Naruto and Kurama weren’t still drained of some. The side-affects aren’t as dire for Kurama as what they are for Naruto, as Kurama is immortal but Naruto is very much human and has a limit to his life-span.
That life-span has been reduced and I’ll try and come up with a number by how much it has been reduced by. As we know, Isshiki had 20 hours left to live when he realized what Naruto was doing and that was reduced to just under 30 minutes. The battle had only just started so, only seconds had passed since the two began to fight. In seconds, Naruto was able to reduce Isshiki’s life-span by 19.5 hours.
If seconds resulted in almost a day, the entire battle should only have affected Naruto with a similar time-frame (assuming he lost the same amount of time as Isshiki) unless, the form worked differently. If only days of your life were shaved off, a man that’s Naruto’s age shouldn’t have much of an issue using the form and Kurama also wouldn’t have been as nervous about accessing that power as what he was.
Therefore, I have a feeling, the transformation reduces the users life-force by differently. Isshiki was set to perish in 20 hours so, let’s pretend Isshiki had 20 years remaining to live for this theory. Naruto is about 33 years of age in Boruto right now and let’s say 73 is the average age of a ninja (naturally). Remember, it’s hard to gauge as most ninja’s die unnaturally in battle but there ones who survive to old age are around that age (outside of Onoki). That means Naruto has roughly 40 years remaining of his life prior to Baryon Mode.
If Baryon Mode took 19.5 hours from Isshiki’s remaining life from him and he has 20 hours remaining, that means 97.5% of of Isshiki’s life was removed. If Naruto’s life was also reduced by that figure, then that means Naruto could only potentially have 1 year left to live, as 97.5% of 40 years is 1 year. Don’t worry though, it’s more likely that Isshiki took on the bulk of the affects so, Naruto should in theory, have more than that.
Furthermore, we know that Naruto was still alive when Kawaki eventually attacks Konoha, at an age when Boruto and Kawaki are in their mid-teens. That means Naruto will be alive in the next 4-5 years. Still though, if Naruto only was dealt with a quarter of the affects that Isshiki had inflicted upon him and assuming Naruto did have 40 years life remaining, that means he could only have 4 years left to live by my math’s and it would allow him to be alive when Kawaki strikes.
This would be how Kawaki over-powers Naruto without enduring much damage himself at that time as well, as Naruto could be on his death-bed at that point. Again, this is all assuming Naruto had 40 years left to live and Baryon Mode removes life-span by percentages. Until we learn more, which we would have in the last chapter when Sasuke asked Naruto about the draw-backs, before Boruto/Momoshiki rudely interrupted, we can only speculate.