The core twist of Aftersun is the realization that the entire film is a retrospective memory-search conducted by adult Sophie, who is now the same age her father was during the trip. The narrative strongly implies that Calum took his own life shortly after this vacation, making it their final time together.
This realization reframes the entire narrative: Calum's purchase of the expensive Turkish rug, his reluctance to celebrate his birthday, his quiet sobbing in the hotel room, and his comment about being surprised he made it to 30 are not just fleeting moments of sadness, but the signs of a man making final preparations to leave the world. He was desperately trying to give his daughter one last perfect memory.
The film's devastating final shot shows Calum putting away the camcorder at the airport, turning around, and walking through a set of double doors straight into the flashing lights of the rave. This confirms that the rave is a manifestation of adult Sophie's grief—a mental void where she tries to catch the fading ghost of her father but ultimately watches him walk away into the darkness forever.