The issue with the game's ending is that, while the player has entered the area where the encounter with Jowan should take place, the quest does not trigger. This is most likely caused by a bug, but it is not currently fixable.

This issue is fixed by editing the UTC file, and assigning a different vanilla morph to Jowan. This will make him appear when the player enters the area where the encounter should take place. This fix is found in this mod, which you can install by simply dropping the tsm_just_one_jowan folder into \BioWare\Dragon Age\packages\core\override.