apparently, it's possible, but they won't remove the Elves either, and Mages are also useful guys... and the Dungeon is just so-so; it's not like in Heroes 1-4, where the Dungeon was really important.
In general, I'm making assumptions based on history. In Heroes 5, the Dungeon was replaced by the Tower. And they appeared sometime... maybe in Heroes 6, it will be a time when the Tower didn't exist yet, and therefore the Dungeon didn't exist either. This means there will be Mages who summoned Beastmen to replace the Orcs. Maybe the Mages will be more evil... who knows
Added 2 minutes later
although I haven't read the chronology of Heroes 5 and don't know when what happened there)
but in my opinion, Mages and Elves are better than the Tower.
God save us everyone
Will we burn inside the fires of a thousand suns...