Yours is a very individualistic view point. The individual can't survive forever, but if you think of humanity as a single living organism, kind of like a mold that has colonized this rock called Earth, then it is immortal. Thinking of it as a single organism allows you to see that, like all life, it keeps itself healthy by having older elements die off while new ones are regenerated. Each individual doesn't matter much.
This point of view is good for thinking environmentally, "we" will live forever as long as we keep the planet habitable. But there's a range of other perspectives between the individual and planet-wide organism. For example, some like to focus on keeping their nation alive, or their race, or their culture, or just their own bloodline. If you elevate any of these it lessens the despair of the inevitable death of the individual.
This point of view is good for thinking environmentally, "we" will live forever as long as we keep the planet habitable. But there's a range of other perspectives between the individual and planet-wide organism. For example, some like to focus on keeping their nation alive, or their race, or their culture, or just their own bloodline. If you elevate any of these it lessens the despair of the inevitable death of the individual.