Let's say that science proves that God exists

[Angrboda]

So, what is this "significant philosophical impact" that you are talking about?

There is a huge philosophical difference between believing the universe was created and designed for human inhabitance and believing that humans are the unintended consequences of mechanistic forces that didn't care whether we existed or not. In the former case humans are elevated to a special status, in the latter case humans are no more significant than anything else that was unintentionally created. We have seen this difference in the human rights of countries that hold to some form of theism and ones that don't.

This is simply false. First, there is nothing about atheism which dictates that one view human existence in any specific light. Moreover, the theist by claiming the existence of a god who is above mankind seems to automatically imply that we are second class citizens and that our needs and wants can never be elevated above those of your god. Moreover, many common brands of theism suggest that our life and existence in this world is of no consequence relative to what is to come afterward. So you've got it precisely backward. It is the theist who devalues human life and meaning, not the atheist. Moreover, no specific worldview or philosophy flows from atheism. Prior to embracing my Hindu traditions, I was a Taoist, an atheistic philosophy which considers life and human existence ultimately good, and is thoroughly concerned with the welfare of people. (The three jewels of Taoism are compassion, humility, and moderation. Mahayana Buddhism is also essentially atheistic and emphasizes compassion for the suffering of others. Jainism is practically fanatical in its concern for the well being of others.)

So, no, you are wrong. If anything, theism is the worldview which treats the worth and value of human life as non-existent.