After she retreated, the mage had joined up with Kolt and his troops but he was too tired to pursue Zach and the others at his full speed. Even if he had been in his top condition, there was no guarantee that he would have been able to catch up to them since they were travelling on trucks which didn't utilize any magic or physical ability. As such there was a high possibility that the mage would have exhausted his magic before catching up to the trucks. Even if he did manage to reach Zach, he would have been too tired to attack them in order to halt their progress.
Therefore, when his lord asked him to move ahead to stop Zach and the others, he could only tell him the truth regarding his condition which annoyed Prince Kolt as it put his entire plan in jeopardy.
"Then you are of no use to me in your condition. You might as well have died trying to kill that slut who caused this." Prince Kolt yelled at the mage as if it was his fault that he was exhausted.
