Years ago, when the Seven Saviors existed amongst the humans, they left several heirs behind to continue their legacy. And those descendants still rule over the Empire which the Seven Heroes formed.
The Inferno Warden was the same. Before sacrificing his humanity for more power, he left several children behind so that in the future, they could manage the Empire, which goes by the name—Emberclad Empire.
However, what very few people know about the Warden is that even after ascending into his Elemental form, he had a child. The mother of that child was none other than the Sage, who was responsible for looking over the Warden.
The reason why the great Elementalist disappeared was not because his flame was exhausted. Rather, he disintegrated himself in the grief of losing his lover when she gave birth to his child.