Okay, after a completely broken game, a day of trying to clean my computer of all Heroes files, re-downloading my version from Google Drive, and additional attempts to figure out what was wrong (the catch was that the Estonian didn't show everything in the video; I found a point in Zakhar's 2.3 guide that says about 2 Zip files and where they need to be installed), I finally got it working!

BUT! Smooth shading has disappeared... and that's extremely important. Those who have uploaded their models, please share how you managed to get it working? Maybe something needs to be done additionally in Maya? I've never worked with Maya before and only did the rigging there following the Estonian's tutorial.