The film's ending ignores some of the events of the film that really merited more attention. Namely, the fact that there's another Lisa who's dead. How are they going to explain that to her employers/friends/family? Also, the bodies of Future Nick, Robertson and Matt were left behind in 1777 along with the wreckage of a plane. That has some serious implications for the course of history (even though it doesn't appear that anything has changed in the present).
I think the movie implied because past Nick never took JK Robinson to the future, they were never killed in the past.
What happened to Robertson's plane? Well, how much of it was made of aluminum? Cause at that point in history, aluminum was worth more than gold.
