Lucifer was right in his worry that Chloe might never come back at all. As the summer draws to a close and the new school year approaches, Dan gets a call from his ex-wife informing him that she has decided to stay in Italy, and has already found a job there. Everybody at the precinct, including Dan, thinks that it's Chloe's reaction to the whole Pierce debacle.
After a lot of arguing, Trixie ends up back in LA and living with her dad, because she doesn't want to give up her friends there. Chloe thinks she's talking only about her human friends from school. Trixie doesn't correct her, but she's also missing Maze and Lucifer.
Dan finds himself somewhat overwhelmed at being a single parent all of a sudden, especially since he is still grieving for Charlotte. In the end, Maze ends up helping him, since she and Trixie made up the moment the girl returned. And Lucifer helps, too. He becomes Dan's new partner, and to both their surprise they work very well together.
When Chloe hears about the renewed (and increased) presence of Maze and Lucifer in her daughter's life, she is not happy, but she also cannot bring herself to tell Dan why she doesn't want them around Trixie.