The original Assassin's Creed ending saw Desmond Miles escape Earth in "a freaking spaceship"

The Assassin's Creed series was originally planned to end with protagonist Desmond Miles going to space to start a new civilization.

As outlined by Eurogamer, digital media culture student Lars de Wildt interviewed a number of Ubisoft developers in 2019 for their article 'Marketable religion: How game company Ubisoft commodified religion for a global audience'. 

In a footnote within that article, de Wilt says that they pieced together an "original plan" for the end of the series, stating that "briefly put, the third game would end with a resolution of the conflict in the present day, with Desmond Miles [...] taking down Abstergo using the combined knowledge and skills of all his ancestors, including AC1's Altair and AC2's Ezio."

Desmond wouldn't only be taking down Abstergo, however, but fleeing from the end of the world - the third game would have been set in 2012, coinciding with the end of the Mayan Long Count calendar - in what original creator Patrice Desilet described as "a freaking spaceship." Desmond would have gone into the unknown with ally Lucy - who was named for the famous Australopithecus fossil - to allow the pair to act as the Adam & Eve of a new civilization.

These plans exist from a time when Assassin's Creed was still intended as a trilogy, and never came to pass. Desmond's story did wrap at the end of the third game, but that only happened after Ezio had played out his own trilogy, and Desilet had departed Ubisoft. Even Lucy had long-since been shuffled off this mortal coil, and Abstergo remains a notable series antagonist today, even after a total of twelve mainline games and a number of spin-offs.

The past looks very different to original plans, but Assassin's Creed Infinity is the future of the series.