this is not the first time History Channel has aired this series. I caught it the first time through and it is pretty interesting imo. They follow several major cities and landmarks and their simulated condition as they go through the years.
As far as what might end humanity on this planet...well we certainly have the nuclear capability to do so, but if one were to consider the scenario in Fallout for instance, even in that extreme case humanity still survived.
I think it is possible for humanity to destroy itself but I would agree with others who have said that its destruction is far more likely from natural means such as objects from space, or perhaps some extreme disaster.
"You'll find that many of the truths we cling to depend greatly on our own point of view."