To be honest, there isn't a clear answer for this one. It all depends on Kishimoto (the Mangaka), whether he revives Kurama or lets him rest in peace. As for the fan theories, there are quite a few. Some believe that Kurama might be able to revive itself once the amount of chakra to maintain its body gets reformed. In contrast, others believe that Kurama's passing was permanent, and we won't be seeing any more of our beloved Kitsune.