Я знайшов на реддіті солюшн:
Found a solution that seemed to finally fix it(at least for now). At least I managed to get all the way to chemical plant(like, the ward occupied building itself, not just location entrance, which before autofailed the quest regardless, even if you left it hanging without doing 2nd defense) and proceed with next story objective without triggering Zalissya fall.
What I had to do:
Finish the 2nd defense properly, leave Zalissya, but return after hearing "Zalissya is safe" message. It will be functioning fully with all traders and stuff. Then in console do
UETools_Ghost (so you don't get killed by following commands)
UETools_TeleportTo (just like this with no coordinates)
UETools_TeleportTo 783729.06, 756685.00, 1621.93 (tp to clear sky base, but I assume any remote location might suffice)
UETools_TeleportTo 401922.22, 549398.50, 698.31 (tp back to zalissya)
and finally UETools_Walk
After doing all that I could leave lesser zone and proceed with main story just fine. Guess forcing location to reload clears whatever it is that forces quest fail or something. Idk why it works exactly, but it certainly does.
