The reason he vanished from the fight and hid himself after a certain point, that he then waited for the enemy third division to barely have any remaining mana left, so that they could not detect his presence under the bridge. And he also had to wait for the moment when Heinz's division would push back the enemy's first division further on the bridge. So that he could smoothly duck under it without any enemy Seekers seeing or sensing him.
After all, because of the communication bands, if just one seeker saw it, this would be relayed to their division leader, and then it would reach their commander in no time. So, the entire thing had to be discreet, otherwise the enemy would not let him reach the opposite side.
