I won because I stripped the general of his artifacts, and before he could reach the Orcish Fortress, another hero who was nearby took the troops, changed some of their upgrades, and returned them. In principle, I could have run to the Orcish Fortress and the Temple with 10% health remaining; I should have made it. I was planning to reach the Mentor.
I didn't make it because after Cana, there were 2-3 turns, and the default hero was on a ship, and in red boots, he couldn't reach the Mentor in time (fortunately, the Orcish Fortress helped). There was also an unnecessary Chaos magic instead of Darkness.