Probably by the time the progeny get back to Earth the current species will have self-annihilated and the earth would have returned to a more peaceful place, th

Probably by the time the progeny get back to Earth the current species will have self-annihilated and the earth would have returned to a more peaceful place, the atmosphere recovered, the vegetation replacing the asphalt and the oceans clean and pure. A few thousands years peace is exactly what the Earth needs.