As far as I know, there is no Hard turn limit but you can lose the game by being defeated or if the doom counter fills up. There are number of ways to lower (or raise, one of the classes gets more bonuses higher the counter is at) the doom counter. At least normal or below doom counter settings it should be possible to prevent the counter from filling up indefinately as long as you prevent Sorcerer King from destroying too many magical shards.

Thank you for the feedback. :)