You may be right. But evolution requires there to be selection pressure. Does such pressure exist today? Any human living in a Western democracy can have offspring without worry of the birth canal being too narrow; one or more members of the family being eaten by wolves; Diseases; I mean, the environment in which modern humans presently exist is just so radically different from that which nearly _ALL _ our ancestors evolved in. Maybe evolution is over!
Maybe you are imagining a future where selection pressure returns - the earth scorches and only those living off-planet survive. But those surviving humans will not have physical characteristics that are well-adapted to their new environment because there were not thousands of years of evolution to mold them.
They will simply have brains that contain the memes (thoughts, skills, behavior) that were needed to get them off-planet.
Personally, I cannot imagine a catastrophe on earth that would make ANY known place in the universe an improvement!