Its unlikely any race would last unchanged for 50 million years. They could likely lose interest in colonizing long before that much time had passed. So the question becomes: how much colonization can one race accomplish before burning out their will to continue?
Just 2 million years ago, human ancestors were small-brained apemen. A million years is a long time.
Even if most lose their interest in colonization, there would still be some interested in colonization, and those would do so. Unless there were some enforcement mechanism to stop potential settlers from leaving.
Just 2 million years ago, human ancestors were small-brained apemen. A million years is a long time.