First, the premise of your question regarding the ability to create more intelligent humans is very much in doubt. Regardless, I’m going to paint a grim, but true picture of humanity’s future for you. It’s a bit depressing.

Humans are not immortal. I don’t think this will ever change. Even our capacity to store the experiences we’ve gained throughout our lives is reaching limits of our brains. So, even if we could dramatically increase our lifetimes, the person we would be at, say 500 years old, would not retain the memory of the person we were at, say 100 years old. So, is this the same person? No, just like you at age 50 are not who you were at age 10. So, let’s agree that a single person cannot stay the same.

What about people as a group? The human species is not immortal. We are still evolving.[1] What we will be hundreds of million years from now will not be what we are today, just like we’re not what “we” were hundreds of millions of years ago. Just take a look at 1.8 million years ago to find “homo erectus”. Humans will not be around in the future. Some evolutionary future form called something else will be. So, let’s agree that people as a group cannot stay the same.

The Earth and Sun will not last forever. “The most probable fate of the planet is absorption by the Sun in about 7.5 billion years.”[2] We need to leave. Or, more precisely, the people of the future need to leave. So, let’s agree that we cannot stay in this same place circling the Sun for all eternity.

Space is cold and cropless. We would need to build impractically huge spaceships to carry plants and livestock to support a large enough biological population that can prevent gene pool issues. (See this set of Quora answers.) Our soft bodies would need to evolve even further to adapt to the harsh environment of space. This may not be practical within either the time or biological constraints. Maybe we manage to turn Earth into a spaceship. Still, without the Sun, it will not have the energy resources to survive. So, let’s agree the existential challenges faced by biological people may be insurmountable in the far future.

We can find rocks in space, but it’s extremely unlikely to find food. (That means life!) Machines, on the other hand, don’t need to kill life to eat. Rocks provide the raw materials they need to increase their population. Their energy can come from light, nuclear, or any electrical production sources. They use less resources overall.

True intelligent machines are our evolutionary progeny. Only they can carry our cultures, history, and knowledge to the cosmos.

But, the existential threat doesn’t end there. The Universe will also end. Whether this happens many billions of years from now, or much sooner, the end means complete annihilation of all that would exist at that time, but also any trace of what ever existed before. If there is some way to escape this, it should be far easier for machine intelligences to discover than biological ones.