At the end of A Simple Favor (2018), the mystery surrounding Emily's disappearance is resolved with several twists: Spoiler Alert!

• It is revealed that Emily orchestrated her own disappearance to escape her controlling husband, Sean.
• Emily faked her death and went into hiding with the help of her friend Stephanie.
• Stephanie, who initially seemed like an innocent friend, is revealed to have been complicit in Emily's plan and had her own motives.
• The film ends with Emily and Stephanie confronting Sean, leading to his arrest.
• Stephanie writes a book about the whole ordeal, and the story closes with a sense of dark humor and irony, highlighting the complex friendship between the two women.

If you'd like, I can provide a more detailed summary or analysis!