If Terraria suddenly becomes real, I would instantly work to get the power similar to that of my ultimate endgame character, then help the Corruption/Crimson and Hallow spread across the world, destroying civilization as we know it, so it can be rebuilt by the Terrarian Elite. I would build a great fortress for myself and a small village that people can live in under my protection from the horrific forces of Corrupt nature if they pay their taxes. They would even gain low tier equipment like Silver/Tugsten or Gold/Platinum, just strong enough to protect themselves from the Corruption/Hallow Monsters, but not strong enough to pose a threat to me. I could even make a hierarchy system based on the skill and knowledge of the people, and only allow those I trust and that have shown me their abilities to live in my fortress and have Frost Armor, a Dao of Pow, and a Megashark.
For those who are also genre savvy about Terraria and gain the same power I have, I would not interfere with their business as long as they don't attack me, my land, or those under my protection. My nation would exist alongside theirs, we could even form a Confederation of the Terrarian Elite if they share my interest of allowing the Corruption and Hallow to dominate nature while we rule over this nature.
The interesting question would be if the Hallow spawns in the Americas, Europe/Asia/Africa, Australia, or Antarctica after the Wall of Flesh is killed. With Wings of your own and Frostspark boots, it wouldn't be too difficult to travel from continent to continent so I could make my nation anywhere outside my home country.