off (one, someone, or something) goes
Said as one, someone, or something is in the process of departing. A: "The plane is taking off!" B: "Off we go on the adventure of a lifetime!" "Off she goes," Dan muttered, as he watched his baby girl drive away to begin her first semester of college.
off someone or something goes
someone or something is leaving. (Said on the departure of someone or something.) It's time to leave. Off I go. Sally looked at the airplane taking off and said, "Off it goes."