However the Manga ends regarding the biju (if they will be united and form the Juby or still be 9 separate entities) even if Naruto looses Kurama, or doesn't become the jink of the Jubi, he is still friends with Kurama and he other tailed beats so i am pretty sure if he needed their help it wouldn't be a problem, like signing some kind of summoning contract and be able to summon them, kinda like how Madara can summon the Kiuby.
But even if we take the biju out of the picture completely Naruto still rocks, remember he has Sage mode, and as someone said during Pain's invasion (don't remember who right now) with SM Naruto is in a whole other league. So he could just focus on developing new Sage jutsu.
Also even without Kurama he still has a ton of chakra so he could still use the Kagebunshin method of training, thus being able to master many jutsu. Furthermore in the latest chapters he has shown just how proficient he is with chakra manipulation so this wouldn't be a problem anymore, i mean molding the chakra the proper way and most efficient in order to use a jutsu.