According to Ubisoft, Assassin’s Creed doesn’t really have an ending. They intend to simply tell the story of the Assassin’s and the Templars until people stop purchasing the game.
Assassin’s Creed Revelations and Black Flag lead writer Darby McDevitt asks us to think of the Assassin’s Creed universe like Doctor Who . Instead of working toward an eventual ending, the games will simply continue to tell stories set in the universe until people get bored of it. Well? Are you sick of the doctor yet? We certainly aren’t, nor are we sick of the Assassin’s so it looks like we will be seeing this series go on for some time.
Unfortunately, there has been quite a bit of reconning in the series since it first came out. “The problem with the Desmond trilogy was that back in 2007 they set a date with Abstergo launching a satellite that was going to control people’s minds,” McDevitt said. “That unfortunately took a back seat in ACII when they swapped the plot point for the end of the world, which was conveniently going to happen in the same month in 2012. This was a hard date we were going to hit–we realised very quickly that Assassin’s Creed is a popular franchise and we’d like to keep it going.”
Source: Edge