Ubisoft Have Plans for Assassin's Creed Ending

To be honest, as with most mass-media, the chances of it just going on and on until people get sick of it and they just suddenly stop making it is far more likely than it ever actually reaching that conclusion.

Realistically I think the general public will never get to see how Assassin's Creed ends. If it's too unpopular to get another game in the series, there won't be another game at all. Simple as.