Complex sentence: The Atlanteans returned to the present along with Manitou's past self, while the destruction of Atlantis in the past ended Gamemnae's attempt to conquer Earth, leaving Atlantis submerged once again and her dead.
Split into simpler sentences: The Atlanteans returned to the present along with Manitou's past self. The destruction of Atlantis in the past ended Gamemnae's attempt to conquer Earth, leaving Atlantis submerged once again and her dead.