 CONT: At the end of the movie, when Marty says the car is wrecked,  they all look out the door and see Biff waxing the BMW, with Biffs  pickup beside it. He is just starting the second coat of wax. After  Marty meets Jennifer they look at his parents behind the screen  door. The BMW is between them and his parents, but Biffs pickup is  no longer visible. Biff didnt leave (he still had the second coat  to apply). In the second film Biff is still at the house when the  flying De Lorean takes off.