> I feel terror at the idea of all of our species on one planet with no backup.

While I would like to live out the rest of my life as best as I could, and I hope everyone alive and not yet alive gets that chance too, I don't think it would be that great a tragedy if humankind no longer existed. Imagine a world where everyone is hooked up to a simulation that feels as real as real life and everyone gets to live out the best possible life (or even lives) for them. They can have as many (AI) children they want in the simulation and never even know they weren't real. In that world, where no one ever had real children again and humanity naturally died out, would that be a bad thing? Humanity is not providing any benefit except to itself.