If he or she finds the original ball before the player makes another stroke with the provisional ball the player must abandon the provisional ball and continue with the original ball. However, if the player makes another stroke with the provisional ball before the original ball is found, it becomes the ball in play because it was nearer the hole than the estimated spot of the original ball (Rule 18.3c(2)).
I think if you find you original before you hit a second shot with your provisional you're supposed to abandon the provisional and resume play with your original. That's my understanding at least.