The problem I think you are highlighting infects THE TERMINATOR – John Connor sends a soldier back in time to stop a Terminator killing Sarah, his mother, before she falls pregnant with John. We know the Terminator doesn’t succeed because John Connor is still alive in the future (otherwise he wouldn’t have been able to send a soldier back in time – Grandfather Paradox, anybody?). So, as you said, we know the outcome before the movie starts, so where’s the suspense? But the movie was a massive hit and spawned one of cinema’s biggest franchises.

Let me try to explain my story in a little more detail…

The pregnant mother travels into the future to when her son is a fully grown man (the terrorist) and the government in that future world wants to terminate her pregnancy to wipe out the son’s entire existence.

So the pregnant mother and her adult son exist in the same time-frame (he’s the fetus in her womb as well as a fully grown adult). He will go on existing in that time until the government catches his mother and terminates her pregnancy. If, like the Terminator, the government sent somebody back in time to kill her, then the son wouldn’t exist in the future. Yet, because they both exist in the same time-frame, and all the action happens within that time-frame, the son can continue to exist until her pregnancy is terminated. A paradox, I know, but I love the irony.

If you look at time as one strand that’s happening at the same moment (as some scientists are beginning to view it), then your argument stands up – if the son exists at the beginning of the story then we know that the pregnancy isn’t terminated at the end, and vice versa, if the pregnancy is terminated at the end of the story then the son cannot exist at the beginning of the story. But the events I depict are within the world of cinema and some suspension of disbelief is required. If we pedantically glue the principles of quantum physics to all time travel stories, then very few of them would make logical sense.