You said it yourself: "having an effect on our physical reality". It is a binary relation: something exists because we can experience it or deduce it from other things we experience.

In your hypothetical example, the existence a planet after it has eg exited our visible universe (because of the rapid expansion of the universe) is only relevant to us because we were able to deduce it from previous observations. Same with things in the past. So to answer your question, since we observe the Earth now, we can deduce its continued existence even after a cataclysm that would wipe out all life on Earth. We could be wrong in our extrapolation. Maybe the Earth would be hit by an asteroid later and things would be different in a way no one imagined. But, without conscious observers at that point, that state of affairs would be not unlike physics in that parallel universe. In that case, according to your definition, it wouldn't exist.