As Hagoromo already confirmed, Naruto will always have the bijuu chakra.
And thus he could still access their chakra at will and use their abilities along with the fully powered war arc RSM mode.
Manga already shows two ways in which he could replenish the bijuu's chakra after they willingly gave him their chakra.
1. Using the Mini bijuu entities (chakra) he received from the other 8 bijuus.
2. By asking the actual bijuus themselves to transmit their chakra remotely
These two methods combined could grant Naruto an endless source of chakra during battle. Though Naruto never had to rely on the 8 bijuu's chakra after the war ended cuz none of the opponents managed to push him that far. At best he used his Kurama So6P mode vs Momo and that's all.
Thank you and Naruto Uzumaki > your fav.
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And thus he could still access their chakra at will and use their abilities along with the fully powered war arc RSM mode.
Manga already shows two ways in which he could replenish the bijuu's chakra after they willingly gave him their chakra.
1. Using the Mini bijuu entities (chakra) he received from the other 8 bijuus.
Lets see how he accessed the bijuu's abilities during war arc:
The first time vs Madara when he used the Lava RS
Then a second time again vs Madara when he used the magnet style Rasengan with Shukaku's chakra
The third time he used the Kokuo's boil release ability vs Kaguya
All the above instances clearly show that the bijuu's exist as separate entities within Naruto with a conciousness of their own independent of the main bijuu and the ability to provide Naruto their chakra and abilities just like Yin and Yang Kurama inside Minato and Naruto respectively. And during all these instances the main bijuu's chakra and their conciousness was merged into Juubi and sealed within their respective jins.
So if Naruto ever runs out of the bijuu's chakra, these independent mini bijuu entities could always generate and provide him with more chakra just like yin and yang Kurama did to Minato and Naruto.
The first time vs Madara when he used the Lava RS
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Then a second time again vs Madara when he used the magnet style Rasengan with Shukaku's chakra
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The third time he used the Kokuo's boil release ability vs Kaguya
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All the above instances clearly show that the bijuu's exist as separate entities within Naruto with a conciousness of their own independent of the main bijuu and the ability to provide Naruto their chakra and abilities just like Yin and Yang Kurama inside Minato and Naruto respectively. And during all these instances the main bijuu's chakra and their conciousness was merged into Juubi and sealed within their respective jins.
So if Naruto ever runs out of the bijuu's chakra, these independent mini bijuu entities could always generate and provide him with more chakra just like yin and yang Kurama did to Minato and Naruto.
2. By asking the actual bijuus themselves to transmit their chakra remotely
We've already seen Naruto do this during the war arc when he passed his chakra to the shinobi alliance and replenished it back remotely without any physical contact when he received more chakra from yin Kurama.
Naruto could do the same and always ask for more chakra from the bijuus if he ever needs their chakra in a hurry after exhausting his own 8 bijuu chakra reserves as long as those bijuus maintain their individuality. And Naruto being the meeting place for the bijuus means he could ask them and receive the chakra without even having to wait in the middle of a battle.
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Naruto could do the same and always ask for more chakra from the bijuus if he ever needs their chakra in a hurry after exhausting his own 8 bijuu chakra reserves as long as those bijuus maintain their individuality. And Naruto being the meeting place for the bijuus means he could ask them and receive the chakra without even having to wait in the middle of a battle.
These two methods combined could grant Naruto an endless source of chakra during battle. Though Naruto never had to rely on the 8 bijuu's chakra after the war ended cuz none of the opponents managed to push him that far. At best he used his Kurama So6P mode vs Momo and that's all.
Thank you and Naruto Uzumaki > your fav.