How is Dark Messiah connected to Heroes of Might and Magic?

In that video, Biara was in the form of Isabel! And the real queen was in the Dungeon with Railag at that time.
There might not be any chances, but he himself said in the second part that he was going to war with the Evil Messiah, wanting to stop him before his demonic essence awakened, but he disappeared for some reason.
I'm all for a role-playing game based on the Heroes universe, or something like Dark Messiah. I would gladly play it. At the same time, we could find out what happened to Railag. There are many inconsistencies and loose ends in the game's plot. For example, how did Biara turn into Isabel, and no one noticed, if Godric was going to take the queen with him to the Empire? How did it happen that Isabel left with Railag without anyone knowing, and Godric brought a fake queen? Or why did Railag say that he was going to kill the Messiah, but disappeared? Or why wasn't Sareth, who was born, immediately cleansed and killed? Where did he go if he was born in the presence of Railag himself? Was Sareth saved by demons? Was the queen kidnapped again? It's unclear... I've been trying to find answers to these questions for a long time.

Added 1 minute ago

But where did she go after Shio????
Well, when they defeated Kha-Belekh........
And the words Xana used to revive Sareth... How is that also a benefit???

I agree! Xana loved Sareth! And Isabel finally fell in love with Railag and returned with him to Igg-Shail, which I just wrote about in the comment above.