At the end of *The Exorcist*, after a brutal and harrowing battle, the demon Pazuzu is finally expelled from Regan's body. This is achieved through a combination of a powerful exorcism ritual performed by Father Damien Karras and Father Lankester Merrin, and Regan's own will to fight for her soul.
The exorcism leaves Regan physically and emotionally scarred, but she is now free from the demonic possession. However, the cost is high. Father Merrin dies from the strain of the exorcism, and Father Karras sacrifices himself by jumping out of a window with the demon, taking it down with him.
The film ends with a scene of Regan's mother, Chris, looking out at the sunrise, seemingly relieved but still deeply affected by the ordeal. There's a sense of both hope and sadness, highlighting the enduring impact of the demonic possession and the sacrifices made to overcome it.
The ending leaves the audience with a powerful and disturbing message about the nature of good and evil, and the strength of human will in the face of overwhelming darkness.