The winner is the first to have two victory points. You win at the moment you score your second point. There are two ways to score a point:

Treasure. If you have an enemy Treasure on your Lair, you have a victory point. But note that if the treasure is removed, you lose that point again!

Kills. If you kill an enemy, you get one victory point. To kill a foe, you must take away their last life point. This can be direct (with a fireball, for instance) or indirect (destroying a wall next to them).

Thus, you can win the game with two stolen treasures, two kills, or one of each. You can lose Wiz-War before the end of the game. If your life points go to 0, you are dead. You also win if all your foes are out, even if you did not get two victory points.