Technological progress is not a given. Spaceships don't magically get built given enough time. Humans must spend effort on it.
Do we really have 50 million years? Very unlikely. Do we even have 150 years? I'd take odds against, we've just come way too close to all-out nuclear war recently and international relations are not trending in a promising direction.
If humanity is at risk of extinction due to nuclear war, then going to space isn’t actually going to accomplish anything; the ISS, nor a Mars colony, nor a city of 10 million orbiting Io are going to be able to stop nuclear war either.
Exactly, humans having developed the technology to destroy earth, will easily destroy any kind of spacial colony. Going to other planets is not a solution at all.
Do we really have 50 million years? Very unlikely. Do we even have 150 years? I'd take odds against, we've just come way too close to all-out nuclear war recently and international relations are not trending in a promising direction.