Don't worry, Marty. Assuming we succeed in our mission, this alternate 1985 will be changed back into the real 1985, instantaneously transforming around Jennifer and Einie.
9 seconds sound clip from the Back to the Future Part II movie soundboard.
You can hear this line at 01:02:03.645 in the Blu-ray version of the movie.
Quote context
[...]
- Damn! Got to fix that thing.
- All right. Time circuits on.
- What do you mean, time circuits on? Doc, we're not going back now!
- Yep.
- Doc, what about Jennifer? What about Einstein? We can't just leave them here.
- Jennifer and Einie will be fine, and they will have absolutely no memory of this horrible place.
- Doc. What if we don't succeed?
- Oh, this is heavy, Doc. I mean, it's like I was just here yesterday.
- You were here yesterday, Marty. You were. Amazing, isn't it?
[...]