It looks like everything that lives is part of the same very extended family tree with a last universal common ancestor at its base. In order to definitely not get a modern Mitochondrial Eve, you’d need human populations that are absolutely independent (and viable) forever. Humanity’s (present) Mitochondrial Eve is not our unique common ancestor nor is she our most recent common ancestor. Mitochondrial Eve is merely the most recent ancestor of all living people by means of a direct female line alone. An important fact to keep in mind is that a huge fraction of the people alive today will eventually be a common ancestor to all of humanity.