If the humans that live today, you me, and evryone in this forum would be thrown back into year 0 then first of all none of the things that has happened will probably happen.
Since we're not the people who lived at that time, and since we're not them then our kids won't be theyre kids, for example Hitler would never be born, because he has already been born and then there wouldn't be any WW2 since he would have died before the rewinding.
But we would probably still face a new and diffrent WW1 (this would have been the WW3 if we wouldn't have rewinded) and maybe a WW2.
But if it would be the exact same people who lived at that time, then everything would be the same all over again (Think of all the suffering that the world had to live through one more time, without knowing it)
Ouch, lots of text there and some of it probably doesn't make any sense but it's what i think
A person who has lost everything, has no fear of loss.
A person who knows nothing, has nothing to fear.