after we go extinct, nature will reconquer the earth.
Depends on how we go extinct, and what you mean by “nature.” Venus is also “natural” but that way lies an antiseptic, brutally extreme planet with not a drop of life on it.
People, lots of things are natural.
Cf. My thesis: http://scholarworks.gsu.edu/philosophy_theses/37/
And this project: https://www.inkshares.com/projects/techne-investigating-the-state-of-the-art
LOTS of things are natural.
The Committee to Nuke Elysium 