What will happen if the original history is changed is an unknown problem. All the statements are just guesses. We are on a one-way street. Even if history is changed, we may not know it. We don't know the true face of Lushan Mountain, but toward which corner of the mountain.

Of course, we can make some reasonable guesses For example, history has been changed, the present and the future will change, representing science fiction: back to the future.

Another guess is parallel space and infinite universe. Changing history is equivalent to another timeline at that point in time. In layman's terms, our universe is divided into two.

Of course, there can be many guesses, so I won't list them here.