What If Concept Development

I am trying to communicate that if we just left the world, perhaps animals would become the new humans and start to do the things that we as humans do right now. But I'm also showing that if we left the world alone, maybe the natural world would have room to take over and become central once again. I am going to draw a train coming forwards with 3 animals popping out of the door onto the terminal. I will then draw the train terminal sort of decayed and with trees growing from the inside. Maybe a hole at the top of the terminal that lets sunlight in. That would be the only source of color. The rest of my picture will be in the gray scale probably made of the different shades of pencil and maybe some charcoal. If I do the sun idea then I will use colored pencil to make it look accurate but mainly just regular pencils.