Completely disappeared without a trace. And deserters, who should have been brought back from previous installments of Heroes.

It wouldn't hurt to bring back the evil Sorceress, poisonous creatures, mermaids, and sea monsters.
If all of the above were to be reintroduced, it would be necessary to create another dozen races. And there would be half a hundred neutral creatures. Although, that would be cool. You play, you play, and there are always new faces...