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

Regarding the fact that Isabel is a terrible queen, everyone realized this as soon as Nicholas, while dying, appointed Isabel as queen... Godric understood this well, but he couldn't do anything about it...
By the way... How did it happen that Agrael still allowed Saret to fulfill the predetermined fate...? I think he knew very well that after contact with Xa-Beleth, Isabel would become a demon worshiper...
And regarding Xana and Saret... When Arantir killed Saret, it was Xana who revived him, spending part of her power... Isn't that a display of love?