In Back to the Future, when Marty escapes the Libyans using the DeLorean and jumps into 1955, we can see at the end of the movie that the van with the Libyans crashes into the photo booth.
If they remained alive they would keep on chasing Doc and Marty on foot. But that is not the case. We see that Marty-from-the-past and Doc peacefully return to Marty's house.
If the Libyans died then Marty and Doc would become accident witnesses and the police would have a lot of questions for them, including the origin of the plutonium, the suspicious car and the reason why they were at the mall that night. So they would likely hurry up to get out of the mall so the police would not see them. But again, this is not the case. They don't seem to hurry at all and take their time for a little chat about the space-time continuum. Moreover, Doc doesn't even bother to hide his van away from the mall. Instead he uses the DeLorean to take Marty home, leaving his van at the parking lot as evidence.