We die. This is inevitable, and there's absolutely nothing we can do to prevent it. Oh, we can delay it. We can work on all those great gene therapies and telomere extensions and push death further and further back until centenarians become millenarians, but eventually everyone will die. Our bodies will rot, and our consciousnesses — barring some kind of spontaneous quantum entanglement-related transfer to a new body — will cease to exist.
So what can we do? Well, we could just give up. That's certainly what the nihilists want us to do. We could embrace some imaginary deity, which the theists would like. We could ponder new age bullshittery, but that would be just as pointless. So what are the options?
Well — and this is just my insane opinion — we could have some faith in our descendants.
It's really easy to believe humanity is getting more and more stupid. For every discovery of flowing water on Mars, there's a hundred about the moronic Honey Boo Boo, or some vapid airhead who is more plastic than woman. For every video showing the wonders of Jupiter or deep space, there are a hundred on YouTube showing some dumbass cracking his skull against pavement or getting a football in the groin.
But people aren't getting dumber. It's just that the Internet is making it easier for stupid people to expose their idiocy. However, there are still many, many, intelligent people here, and it is they who are making our James Webb Telescopes, designing our quantum computers, sequencing our DNA, pondering our telomeres, and building the next generation of our robots.
This will only continue. Technology and society will continue to advance. Our ills will not vanish, but we will learn to advance in spite of them, not let them hinder us. We will survive global warming. We will survive terrorism, pollution, greed, corruption. They will slow us down at times, but never stop us.
One day, we will cease being human as we know ourselves now. We will elevate ourselves beyond the need for physical food or water, beyond the need for oxygen or bathing. We will still eat, still have sex, still appear human in many cases. But it will be a case of interest, not necessity. I don't believe it will happen on Kurzweil's timescale, but it will happen.
We will colonize Mercury, Venus, the Moon, Mars, the Jovian moons, Titan...all the worlds of the Solar System. And we won't have to terraform them. Instead we will "terraform" ourselves. In doing so, we will open the door to the Offshooting of humanity. These Offshoots will be as plentiful as there are species of insects or reptiles. Over hundreds, even thousands, of years, these Offshoots will each develop their own cultures and beliefs based on history, literature, film archives, ancient games, or their own imaginations. The people of Mercury could be a race of sophisticated treelike beings, soaking up the intense light of the nearby Sun like a sponge. The fiery dwellers of Venus could be akin to Balrogs, but with a civilization that rivals ancient China's. The gaseous Offshoots of the outer planets would be more wind than solid, but capable of works of such amazing beauty that I can't even picture them.
And eventually, via time or a breakthrough in wormhole technology, we will spread throughout the galaxy. I'm going to be a pessimist here and assume the galaxy is empty of sentient life except for us.
But it won't be for long. Over tens of millennia, our Offshoots and the animals we have manipulated to be human-sentient — cats, dogs, elephants, raccoons, etc — will colonize billions of worlds. And though progress will be interrupted by terrible wars, plagues, societal collapses, and other disasters, we will survive. And one day, our distant descendants will crack the secret to time travel.
I doubt they will be able to physically travel through time. Instead, they will be able to observe all points of time and the peoples within, using advanced technologies to scan the consciousnesses of all those who have died throughout existence, and transfer them to new bodies on worlds uniquely developed for them. All deceased people will retrieved in this way. No God, no Nonexistence. In the end, we will be saved by our own descendants, who have followed the path forged by those who preceded them.
Why would humans of the far future do this? Partly out of curiosity. Why read about historical figures when you can bring them back, learning from them directly? Why wonder about who your ancestors were when you can bring them back? Obviously, there would be security precautions in the case of more...unsavory characters.
Another reason would be to show people like Sagan and Einstein that their work was not in vain, that their ideals prospered and led to an incredible future for humanity. Imagine bringing Sagan back and showing him that humanity has colonized the galaxy. Imagine bringing Einstein back and showing him that humanity is traveling throughout the stars. Imagine bringing Roddenberry back and showing him a duplicate Enterprise that can actually travel throughout the galaxy! Imagine bringing Aldrin and Armstrong back and showing them the Moon's eucumenopolis.
Yet another reason would be simple love. The love of our descendants for their ancestors. In fact, I believe the peoples of the future would feel an ethical duty to bring the deceased back, especially if the nihilist worldview prevails.
Still another reason would be militant in nature. Wars will still rage in this far future, and once Retrieval becomes a reality, governments bent on conquest will see the potential for billions of new troops and workers for their aims. In fact, a brutal war will most likely be fought over control of the Retrieval process.
As I said, this is on a very long timescale, on the order of tens of thousands of years, perhaps hundreds of thousands. But I have no doubt that it will happen eventually. Yes, many things will change, and many societies will give up on the paths that will lead to this outcome. But it will only take one society to succeed.