And then it got even more interesting: the defeated enemy heroes didn't appear in the tavern, the demons didn't come at all, and with each turn, I became more and more convinced that the game was completely glitched and I would have to start over (honestly, I would have just given up then, I didn't have the strength anymore), but fortunately, after capturing the last city of the enemy, the script finally worked, and the mission was finally completed... And the demons... well, they didn't come, and that's fine, let them suffer.
I haven't reached Nikolai yet, so I don't know how difficult it will be. I've just started the campaign for the light elves.
At the same time, I want to thank everyone who shares their experiences and advice on the forums.