Doc: "All right, time circuits on."
Marty: "What do you mean, time circuits on? Doc, we're not going back now?"
Marty: "What about Jennifer? What about Einstein? We can't just leave them here."
Doc: "Don't worry, Marty. Assuming we succeed on our mission, this alternate 1985 will be changed back into the real 1985, instantaneously transforming around Jennifer and Einie. Jennifer and Einie will be fine, and they will have absolutely no memory of this horrible place."
Marty: "Doc, what if we don't succeed?"
Doc: "We must succeed."