Within a couple of hundreds of millions of years from now, the Sun will become so bright that it will boil the Earth, guaranteed to kill all complex life on Earth.

To be more specific, its more like 600-1000 million years.

When considering how quickly humanity has advanced technologically in the past several centurys alone, it is difficult to imagine what they might achieve in several millenia. Especially when realising that the Earth will be ruled by superintelligent agents by then. Civilisation is only about 2500 years old, imagine what it might achieve after 10,000 years. Technologys such as Dyson spheres are utterly impossible with our current technology, but who knows what might happen in several millenia.

If a civilisation can build a Dyson sphere, then they can influence the evolution of their own home star. There is a hypothetical process called star lifting whereby a portion of a stars mass can be removed from its surface, which lessens the gravitational pressure on its core, which consequently reduces the amount of hydrogen the star must burn. Star lifting could extend the lifespan of a main sequence star far beyond what would normally be possible. It sounds insane, but it doesn't violate the laws of physics.