This has all happened before. And will happen again.
We originated on Earth. We built sentient machines. They rebelled. We had a mass exodus from a ruined Earth and settled on Kobol. The cycle repeats and humanity abandons Koblol and settle in the 12 colonies. A splinter Cylon group settles back on an Earth that has recovered from the previous disaster.
The cycle repeats again two times - on Earth and the 12 Colonies. The Final Five leave a charred Earth and head to the colonies. They meet the Cylons, exchange resurrection for an end to the war.
The cycle repeats once more with the nuking of the Colonies. Humanity, pursued by Cylons once again returns to Earth.
I think that's where we are. Further, I think the series will end with the survivors settling on Earth.