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

I think these heroes should remain as they are. Why force something in? Do you miss the third game? The third game is great – I agree. But what did the fifth game do wrong? They already have enough dragons (if you add any, they should be mythical ones, and only as neutral creatures, for aesthetic purposes).
And the Swamp race doesn't fit here at all.