You cant change anything about the world. Whatever fate it faces you must face too. Take it how it is... however you can be whatever species from the planet youd like to be(so if you wanna be a spartan, go ahead!). It would be a hard choice for me. Iv always thought Rapture would be amazing, but its dark story and demise discourage me. So im between that and Pandora from Avatar (if im Navi). (Looking for an epic bungie group to join? Join StarSide Echoes! http://www.bungie.net/en/Forum/Post?id=60694890 )