Helaman and his army were able to stay ahead of the pursuing Lamanites. Because the Nephites were heading into the land where they could easily be reinforced, the Lamanite army realized that their attempt had failed. Therefore, they turned to go back to Manti.
Manti was now in Nephite hands, and therefore they did not have a fortified position to return to. However, with their numbers, and the smaller force defending Manti, they might have been able to retake the city. Therefore, Helaman had his army force march around the Lamanite army and return to assist in the defense of Manti.