Project of the Losts; Enceladus

The humanity's empire fell once and for all. The nature is taking its place to the Earth once again. Buildings, roads and everything that humans built is being destroyed and flowers and trees bloom through them. However, while nature prevails in the surface of the Earth, humans hide and expand their empire underneath it. Especially, after their mission to be transferred into Mars and starting over their lives there failed sending more than the half of the population on its doomed, their self-esteem and the trust in science has been destroyed. Will they ever see the sun again? Will they stay underground forever and vanished once and for all? Will they learn their lesson to respect nature? Let's see! (Credit for the picture: https://sergran.artstation.com/projects/D5klDR)