Even if humans manage to survive for millions of years into the future, we've already burned all the easily accessible fossil fuels. What we're burning now takes a lot of technology to extract. It's not immediately obvious that we'll ever be able to become a space faring civilization without cheap fossil fuels to bootstrap us there. Eventually, we'll go extinct by some asteroid impact or supervolcano.
We should probably assume it's now or never for intelligence to spread off this rock.