As Paul states, the dead in Christ, those people who at the time their body died were born again spirit filled believers in and followers of Jesus, rise first.

1 Thessalonians 4:16, "For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first:"

1 Thessalonians 4:17, "Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord."

It is important here to remember that Paul was writing to believers, not to unsaved. This is confirmed by his using a greek word (strongs number 2249 hemeis {hay-mice'}) that translates as 'we', thus including himself. This verse is also conditional...not only those who are alive, but those who are alive AND remain (strongs number 4035 perileipo {per-ee-li'-po}) that translates 'to remain over, to survive'. He is referring to the same people that Jesus is talking about in Revelation when He refers to "He that overcometh". So the people who will be caught up to meet Jesus in the air when He returns will be the people who overcame the devil and temptation. How this overcoming is accoplished is of course: Revelation 12:11, "And they overcame him by the blood of the Lamb, and by the word of their testimony; and they loved not their lives unto the death.". Then the believers will all be changed, transformed, given new glorified bodies like Jesus:

1 Corinthians 15:53, "For this corruptible must put on incorruption, and this mortal must put on immortality.",

and : Romans 8:29, "For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.".

Therefore, that portion of the living who are caught up to meet Jesus in the air are not a problem with respect to anyone with sin getting into heaven, because they are true follwers of Jesus. They love one another as He loved us, thereby fullfilling all of the law and the prophets:

Matthew 22:36-40, "Master, which is the great commandment in the law? Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment. And the second is like unto it, Thou shalt love thy neighbour as thyself. On these two commandments hang all the law and the prophets.".

They also know that 1 John 1:9, "If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.", thus they have NO unrighteousness, but rather they have become the righteousness of God:

2 Corinthians 5:21, "For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him.".

As for the rest of the living, all of those who ultimately do not accept Jesus and live his teachings, will either die in their sins and await the judgment, or be among the last group that is deceived by satan and are gathered together to battle against the saints.

Revelation 20:7-9, "And when the thousand years are expired, Satan shall be loosed out of his prison, And shall go out to deceive the nations which are in the four quarters of the earth, Gog and Magog, to gather them together to battle: the number of whom is as the sand of the sea. And they went up on the breadth of the earth, and compassed the camp of the saints about, and the beloved city: and fire came down from God out of heaven, and devoured them.".

This is just before the great white throne judgement. So all of the truly saved are either raised or caught up, and all of the unsaved are dead. This is the judgement that is spoken of in Hebrews 9:27, "And as it is appointed unto men once to die, but after this the judgment:".

Revelation 20:11-15, "And I saw a great white throne, and him that sat on it, from whose face the earth and the heaven fled away; and there was found no place for them. And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works. And the sea gave up the dead which were in it; and death and hell delivered up the dead which were in them: and they were judged every man according to their works. And death and hell were cast into the lake of fire. This is the second death . And whosoever was not found written in the book of life was cast into the lake of fire.".

So at the last, it comes down not to whether a person has committed this or that sin, but rather has that person repented of that sin (all sin in fact) and made the decision to live for Jesus, by the spirit of the living God, having their names written in the book of life.

The judgement of the living then is at the time of Jesus' return and those in Christ who are alive and remain and are overcomers at that time are raised. The ones who are not either raised or caught up at that time are still given the chance to repent of their sins, though large numbers will not do so despite the obvious outpouring of the wrath of God in the 21 judgements prophesied in Revelation.

Recently someone presented a hypothetical dialog between satan and his fallen angels where he's talking about having lost in heaven, and lost at calvary, yet having one more chance to compel God to let him and his angels back into heaven. However,God speaking by the prophet Isaiah makes it clear to me that the only way satan would even want to return to heaven is as a conquerer, taking the throne of God for his own:

Isaiah 14:12-15, "How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations! For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north: I will ascend above the heights of the clouds; I will be like the most High. Yet thou shalt be brought down to hell, to the sides of the pit.". satan does not want to simply be re-admited to take his former position and certainly not any lesser place. His desire is to rule all.