RTF is a global modification that replaces all towns in the game.

Official source or a recording of that presentation, please!!!

And in general, in this case, it is necessary to leave the demons in the game, and such an ending is clearly nonsense! - the demons are finally freed, the most patient of the inhabitants of Ashan rejoices! (I'm talking about the Overlord) and finally they can... just sit in Sheogh and forget about Ashan... - what, excuse me?! and the Order of Void appeared again out of nowhere - it seems to me that the person who left that comment misunderstood something or came up with it himself (or it's the "broken telephone" effect) to make such statements and rely on them, concrete, verified data from an official source are needed.

I see it this way: it is possible that Sareth will usurp the throne :) and he probably doesn't want to destroy everything - now he is the king and will rule his people.
And with the Order of Void, it's like this:
1) Lucretia is alive
2) In Heroes 6, Sandro found the Ring of Sin, moved to its dimension, got the Mask of the False Face there, and the WORLD OF THE RING was destroyed because the soul that created this world went to Ashan after losing the mask, and in Heroes 5, the World of the Ring exists, which means a new soul holds its walls, taking into account Sandro's phrase "the ring is now useless, but I will continue to study it," I concluded that Sandro's spirit now lives in the ring and is waiting to be released