He might even be considered a monster after some time when people realized that he was not growing older. He was not sure what would have happened then.
Only one thing was certain. If that world was not destroyed in the war, his future really could have been different.
His sister would have grown older and died. Gabriel would never exist. He wouldn't have to go to the Upper Realm to save his sister.
The other Holy Lords wouldn't have become his enemies. They wouldn't have awakened either, so their world would have been normal, forever remaining unaware about the existence of others worlds.
In that case, he might never have met the Upper Realm's Lord.
The reason Elzeirans were able to open the seal to their universe was because of Gabriel. He brought the Elzeiran Princess to the Upper Realm.
If Gabriel did not exist, and he was still in his world, the seal would not be destroyed either.