RAN OVER BY A TRAIN?
Unless it comes from their distant past/ alternate future, because it's no longer existent from the reality, dimension, universe(whatever) that the movie leaves us at.
Not to say in some parallel universe it doesn't exist simultaneously...
The best we got is a really stupid looking time machine train. Doc didn't seem to like the idea of having a time machine at the end of the movies, yet he had one...but whatever.