How does a boy survive in a magical world?

In the year 20XX, humanity disappeared and appeared in another world with magic, swords and game functions, and there were game missions as well. While humanity was trying to survive in this world, but after several years all living creatures died because of the demon king, but there was a person named Luke who was the strongest warrior in the world, but he died Also, but suddenly Locke went back in time to the day of humanity's transition, what would he do?