Just watched it on Google video, once I figured out that it is called "Life After People." Fascinating stuff for a hypothetical scenario. In all reality though, I think it highly unlikely that all humans would simply die off simultaneously. Difficult as the future may be for humanity, and that includes the possibility of a major die off, human life and civilization in some form will go on for thousands more years.
When I started getting into "doomer" material on the internet back in 2005, I began to realize what amateurs the WTBTS really were in this area. I think it was healthy for me to go through this phase because it helped me to get a grasp on the temporary nature of all things natural and man made. One of the greater myths of our modern culture is that the "empire lasts forever," a belief that groups like Jehovah's Witnesses exploit along with utopian fantasies (Live forever on paradise earth in God's empire, anyone?) to gain followers.
Whereas religious groups rely on ancient texts (Bible) for their authority in the eyes of some people, modern doomers look to the internet, documentaries, and some scientific studies (Final Empire (Koetke), Limits to Growth, "The End of Suburbia," DieOff.org, etc.). However, I feel that some of the more prominent doomers have moderated their approach as time passed as a result of healthy debate (theOilDrum.com). Personally, I am looking at the future with an open ended sense of curiosity. No matter what happens, I just want to live as long and healthy a life as a human can. The only thing I know for a certainty is that there will be no Biblical "End Of The World As We Know It."
Dave