I'm gonna be real with you mammals didn't even exist 250 million years ago. That's how much evolution has happened. In 250 million more, mammals will continue to evolve,
If by some incredible stroke of luck we don't wipe ourselves out, any descendants left at that time won't be human. In fact that's so long that there could be dozens of post human species living all over the galaxy.
There's a theory that we only have one shot at becoming a highly advanced spacefaring species. If we experience global societal collapse where present day knowledge is lost, the remaining resources on Earth we used to arrive at our level of technology won't be available to any that come after. All the special materials were near the surface of the Earth, and we used primitive methods to collect and refine those. We got all of those, but that was okay because we used that to make specialized tools and machines to dig deeper getting to additional supplies of those materials.
the theory goes that humanity, rising from the ashes of the fallen past with technology and knowledge lost, won't have that same chance. They'll be stuck on Earth until the Sun consumes it.
It's not farfetched, it's the most likely, realistic outcome. I think we're already too late, and we've blown our chance these last few decades. This is the deciding era.