Bingo. We need to keep the biosphere stable/habitable and preserve a good amount of biodiversity, but ultimately all species and all of their decendant species will go extinct in a short period of time (on a universal scale).

We have the duty to prevent that if possible. Using near future technology we should be able to at least ensure some life survives the death of our star. Easily imagined technology would let us spread life far enough to survive almost any catastrophe. It will be up to some future life forms to figure out how to escape the heat death of the universe... We can only do so much after all.