Even if it comes to close there are ways it can continue. A different copper maybe who reacts differently going back in time. A different person who has a different job. Going back to a different decade as well. Imagine a GP going back to the 1800s where he has to amputate without anaesthetic and perform medical procedurures/use medicine that he know won't work.
The concept, comparing the past with the present is a really good one, I think they should take it as far as it can go. I am not sure the 80s would work though, as its too recent. Its not really like Life on mars, as it were. Even I can remember the 80s
