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There is a script in the mission. I saw a formula for calculating the arrival of Day X somewhere. From this day on, 666 dragons start arriving for Nicholas every day. Therefore, 5000 is not the limit. Dragon nests bring this day closer. The faster they are destroyed, the longer it will take to arrive. If all the dragon nests are destroyed quickly enough, Day X will never come.
I left the Phoenixes in the nearest town and went to destroy the nests. If you don't take Phoenixes at all, a glitch may occur. After the battle, Nicholas may disappear forever. Then you will have to replay the mission.
My Faidean is so well-leveled that no one attacked him. If a careless Necromancer was caught in an open field, in version 3.0, he would instantly run away from the battlefield without a single shot. In version 1.5, they don't run away from the hero, but that didn't help me much. Without logistics, it is difficult to catch up with enemies running away in an open field. I had to kill them in castles.