It's all messed up and can't be fixed on this side of Armageddon.
Basically, the world under Christ for 1000 years will gives us a historical background of what it is like to be perfect and under one religion and one governement. Even so, look how many rebel against Christ once the 1000 years is over and Satan is let loose again? So all that experience during the 1000 years, plus all the previous close to 6000 years of man's history prior to that under imperfect conditions, myriad of different governments and Satan's influence will all factor in on JUDGMENT DAY. All the outside factors and influences plus affect of imperfection will be removed from individual situations and they wll be judged for their true heart condition. The elect (1,440,000; only 144,000 are natural Jews making up 10% -- Isa. 6:13) will be people who have gone through all the trials of humanity so they will be able to show compassion and understanding. just as a former alcoholic makes a better counselor and will show more understanding to another alcoholic than someone who has never been an alcoholic.
So in the end, anyone truly "righteous" will get life. If the ratios are consistent, thus, the majority of mankind up to 2/3rds of everyone will get life. This is based on, given freedom of choice and free moral agency, that 1/3 of the angels rebelled against God, so I suspect a similar ratio when it comes to mankind.
Basically, one third of today's population will be chosen to live under the millennium of Christ. So everyone has a 1 in 3 chance of surviving Armageddon and living during the millennium. Everyone has a 2 out of 3 chance of surviving Armageddon, but only one third will live on to enjoy the millennium. The other third will die out of old age, not having qualified to enjoy the millennium, but not necessarily a wicked person either! Sort of like Moses making that last mistake and being denied entry into the promised land, etc.