As Stephen Hawking explains, humanity must go into space if we were to save the whole race. A massive meteor could come from anywhere in the near future and hits the earth, destroying all life as we know it. Or, as expected, a World War 3 erupts and destroys civilization with flying nukes.
I always thought that humanity has the capability to live forever as long as there's knowledge and technology. For example, we have the power to stop global warming right now. Or, in our distant future (if humanity could live that long), we invent a time machine that allows us to go back in time before the universe collapses. We have the tools in our hands; we just have to make the right decision to find the right path.