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Checked the save, the situation looks consistently difficult, but not hopeless. It's not great that, besides Tazar, only Gervulf is leveled up, and he's stationed at a location with pits. Another 2-3 heroes with the "Logistics" skill and pathfinding would be very helpful. The Psychics in the center allowed me to level up additional heroes.
Loaded my saves and was surprised by how many flies spawned in 6 months).
Overall, I think that your playthrough, if successfully completed, will be very valuable, as I did use some serious workarounds in the form of those months of farming flies and using Venwell's bugged strategies in a couple of battles with neutrals.