I'm afraid we won't get to see dwarves, at least not without expansions.
Well, elves are a more likely option, especially if you remember the first Heroes game. There weren't any mages there.)
If we consider the storyline, mages are more likely, because it's hard to imagine a campaign for the Necropolis without them. And the whole story could be told.)
And dark elves could easily be released as an expansion, where the whole story about them could be told (as in the case of mages and necromancers). This is more logical.
But if we remember the five heroes for each faction in the campaign, then elves seem more suitable to me.
So the score is 2 - 2.