Let's say that we have a time machine. We take a trip to the past to.. Let's say, kill Hitler. We go back, kill Hitler while his was still a child and return to the present day. But now in this timeline no one knows who was Hitler, and that include us. So if we never knew who was Hitler then we wouldn't have time travelled to kill him in the first place. We created a time paradox. So my quiestion is: what happens now that we have created a time paradox? Will the universe be torn apart? Or will the universe bring things back to normal as they were before we time traveled?
This scenario seems fairly simple. 3 timelines will keep switching with each other.
Timeline 1, the "true" Timeline. Hitler lived, the time traveler decides to go back and enters Timeline 2.
Timeline 2: this one automatically exists the moment you time travel regardless of what you do. Because in Timeline 1 you never traveled back in time and never changed anything. Should you kill Hitler, then you won't make the decision to go back in time but you'll do something else instead.
Timeline 3: you do something else instead, Hitler lives and assuming you didn't do worse things with your "something else", you'll go back in time to kill Hitler, meaning you end up in a loop between Timeline 2 and Timeline 3 while Timeline 1 continuous on without you ever existing in it (if it isn't destroyed that is).
When you look at time travel, there's in effect a dozen different things that could happen (https://www.google.nl/amp/s/amp.space.com/21675-time-travel.html). The way you describe it I would assume a more classical sci-fi interpretation, but these often seem to miss critical parts in their reasoning to make sense.
John Brunner answer this very elegantly in his short novel Times without Number. Each time a time traveler goes back and changes the past there is a risk of changing it so much that time travel is not subsequently discovered. Sooner or later that happens, and now you have an unchanging history.
The conclusion: If time travel can exist, we will still never remember it having been invented -- though we might remember people who claimed to be time travelers from the future visiting us...