In C.S. Lewis's Chronicles of Narnia series, "The Last Battle" is the final book and concludes the story of Narnia. At the end of "The Last Battle," Narnia comes to an end, and the characters move on to a new and more glorious version of Narnia called "Aslan's Country" or the "True Narnia."
The ending of "The Last Battle" suggests that the old Narnia, along with its physical existence, is no more. Aslan's Country is portrayed as a sort of afterlife or heavenly realm, and the characters who were faithful to Aslan (the series' allegorical representation of Jesus Christ) are welcomed there.
Throughout the series, C.S. Lewis uses Narnia as a metaphor for the Christian concept of a temporary world and an eternal one beyond. In this context, it is not expected that humans can return to the old Narnia, as it has served its purpose, and the characters have moved on to their ultimate destination.
In the closing scene of "The Last Battle," the characters find themselves in Aslan's Country, and it is described as a far grander and more beautiful version of Narnia, where they experience eternal joy and fulfillment. While the old Narnia may have passed away, the hope lies in this new, eternal Narnia where the characters find their true home.
In a symbolic sense, the message is that life in this world is temporary, but there is a greater and eternal existence awaiting those who have remained faithful and just. It emphasizes themes of spiritual growth, redemption, and the promise of a higher and everlasting reality beyond the physical world of Narnia.