It is a little misleading to have to go all the way to the end, and even play the audio effect for winning, just to have nothing happen.  It would be much better if it could be cancelled after the battle is won against the sov casting it, or at least at the start of the next turn.  I'm pretty sure your own timer is cancelled if you get defeated before the 10 turns is up, so if the AI sov is cancelled it should do the same thing.

Btw: has anyone had the Spell of Making occur in a game when Spell of Making victory is turned off?  I'm very sure I turned it off but someone still managed to try to cast the Spell of Making.