Walkthroughs for custom maps.

Here is the answer, actually. I said: a single-player walkthrough is not a dogma, but an example of how it can be done. The same applies to fire magic: WSW did not prohibit using it, and only with a very high level of skill and to satisfy one's ego can you complete the game without it.
I tried to finish that day from your save several times, in different ways - it turned out like this: if you move away, the enemy still runs out and kills our heroes, and if you move further down the road - if he can reach you, he will kill you. And only if you run away very far, the enemy does not attack, but also does not come out of the city, he just sits there. I skipped several days, but he still didn't come out, he's lazy. Most likely, it's better to wait and come there later - maybe then it will work out. It's a pity that the heroes don't have Camouflage: you could trick the enemy so that he wouldn't attack.

In the same situation, the computer can run in different directions, especially if there is a choice of where to run (artifacts, resources, mines, external dwellings, etc.). You can simply reload and see where it will run. It's worse if there is no choice of where to run (everything has been taken, there are no mines, etc.). But even here you can play around, sacrificing "random" heroes. Then, after going out and killing 1-2 weak units, the computer may run after your main hero. If it is afraid of the main hero, you can weaken the main hero, for example, by taking away archers or reducing combat stats.

In addition, it has also been noticed that loading the same save, but with HD+ or just HD, and/or with the SoD_SP utility, and/or different versions of the game's executable, the computer may behave differently! Either it attacks, or it just waits.

Therefore, you can also play around with switching game loading modes and catch what you need. This is especially noticeable on custom maps, for example, Ira the Mage, where the computer behaved simply terribly, not according to the Chinese scenarios, it did not want to attack in certain points of the map :)

But specifically on Paragon, in this situation, there were no problems with the computer running out: it ran out and was killed.