Well, all Halo fans know for a fact that humanity will be completely wiped out by The Covenant in year 2561... duh.
But most likely all the Christians will go up to heaven, while all remaining people with other rligious/atheist beliefs will rot in putrid wave of Hell Fire and pestilence. Ta.
But seriously, since this isn't the end of
humanity we're talking about (or are we?), it only makes since that the Earth is screwed once the sun goes all jiggidy.