The alignment in 2012 is with the Earth and Sun in alignment with the Galactic Center.
If there was a civilization(s) extant 25,000 years ago that was destroyed, how would we know that they existed... isn't that what "destroyed" means? Maybe evidence is covered with several miles of ocean - Atlantis, for example, or maybe they lived on a (then) temperate continent of Antartica before the poles flipped or moved and evidence is covered with 2 miles of ice now.
I seem to remember in one of Van Danaken's books a Christopher Columbus era map that showed the coastline of Antartica, passed down thru generations of navigators, that couldn't be confirmed as being correct until 1947. Another map dated 1512 showed the Pacific Coast and interior rivers of South America (correctly) before they were (re?)discovered by Europeans in later decades and centuries.
We won't even get into the Sumerian civilization that may have preceeded the Egyptians by several thousand years, and who were probably the architects of the Great Pyramids and The Sphinx, and the Egyptians merely incompetent imitators, as the architectural prowess of later pyramids devolved, rather than improving. Gilgamesh was trying to find something that was historical to him. So was Alexander the Great.