I dont care about the bolt but kurama return is the only thing that make sense in this story and the explanation date back to shipudden, bijuu are immortals and since kurama still had some chakra left in the world after dead he was able to reform. I am even more happier that its Hima who got to bond with the goat, the bolt already got everything else allong the jutsu (rasengan, hiraishin, chakra chains when?) its only fair to the daughter to get the power of her dad mainly kurama.