She left the convent a long time ago, got involved with Alex Marshall (father of her daughter, Jessica), Don Craig and eventually married Neil Curtis. They ended up getting divorced and she left town. She returned for Tom's funeral, Hope and Bo's wedding (1996), Mickey's funeral (although she wasn't seen onscreen, was just "in the other room"), then Alice's funeral in 2010.
She wrote a letter to the parole board to help get her grandson, Nick Fallon, released in 2012. Jessica actually made a brief appearance for that. Later, when Nick and Gabi got married, Maggie said Marie and Jessica couldn't make it. After Nick was killed, it was mentioned that Marie moved in with (or close to) Jessica ("out East"). Josh (Jessica's husband/Nick's father) hasn't been mentioned in a long time so no idea if the character is still alive.