Trust me with the current technology humans can't destroy Earth and let alone can save it. Even a Mars size object collision can't destroy Earth. Only humans and other lifeforms would be destroyed. Some bacteria would even survive on this collision.

You worry about pollution? Without humans those most polluted river in the world would be crystal clear in less than 200 years. All plastics  would be gone in 200 years time too. Most metals would rust. In 1000 years without human those cities would become Forrest. Humans don't need do anything to save this planet. All we need to do be gone and Our planet can repair itself.