250 million years is an estimate for when the formation of a new supercontinent results in sufficient volcanic activity to drastically increase CO2 in the atmosphere and probably kill off all large mammals. 500 million is when C3 photosynthesis stops being possible and virtually all plants are gone, which would collapse all terrestrial ecosystems and leave behind very little animal life, probably none. There seems to be a very high likelihood of extinction level asteroid strikes happening well before either of these.

But we're talking here about a span of time that is a thousand times longer than anatomically modern humans have existed up to this point. Given how far we've come since then, I don't know how you can possibly speculate what kinds of capabilities we might have by then to synthesize breathable air and food from raw disintegrated atoms of anything. If you look billions of years into the future, then it's going to get hot enough to sterilize the planet of any life whatsoever, which we probably can't overcome. If we can terraform other planets, we can terraform Earth itself, which would seemingly overcome any other challenge short of triple the heat that is eventually coming.

It seems maybe a bit premature to think this is something currently living humans should worry about figuring out how to escape from.

We might also note that, given the compartively short time it took humans to come about after the K-Pg event, it's probably reasonable to expect there is more than enough time before these "possibly all life killer" type far future things happen for some other kind of intelligent life that develops civilization and technology to replace humans if we go extinct by some means other than the planet being totally destroyed.