Well, 'Viva La Vida' seems to explore the complex nature of leadership and the transience of power. It could draw inspiration from historical events or be a symbolic representation of such concepts.
The book contains stories such as those of heroic quests, magical encounters, and personal growth. They all contribute to the overall charm and depth of 'El Libro de la Vida'.
The theme of change and the fall from power in 'Viva la Vida' can be shown through the downfall of Voldemort. His reign of terror is like the brief moment of power in the song, and his defeat is the fall. A fanfiction could explore how the wizarding world rebuilds after his fall, similar to how a new order rises after the events in the song.
One idea could be to have the characters from Harry Potter set in a world where the song 'Viva la Vida' seems to be a prophecy of sorts. For example, Harry could be seen as the 'fallen king' who has to rise again against new threats in the wizarding world, with the lyrics guiding his journey.