They are believers and know what they are doing is against God's word.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
What about the same situation; but no sexual intercourse.
Yes, they will go to heaven. Salvation is determined through accepting Christ not through perfection. Thru salvation our repented sin is forgiven. Not obeying God in this area robs you of His full blessing which He desires to pour out on you. This includes richly blessing your relationship when it lines up with His requirements. In marriage you two will be blessed beyond earthly understanding but outside His will your blessings will only be as good as the world has to offer, which can be painfully empty at times.
I agree that salvation is determined through accepting Christ but that is accepting Christ as "Lord" and if he is Lord then obedience to him is required.
To say, "you are my lord," is to say, "I am your servant," and to say, "you are my king," is to say, "I am your subject."
One cannot say, "you are lord but I will do as I want." To do as one wants is to declare oneself as one's own lord. To declare Christ as lord is to do as Christ wants.
I believe in marriage is a wonderful institution established by God for the stability of the family. However I believe that the situation is different when you have 2 seventy year olds meeting for the first time and committing to each other in love who already have established families (grown children, grand kids) and need the space of their own homes to care for and support their respective families. Fornication to me, rightly or wrongly, is sexual immorality where one has several partners on the go, similar to the behavior (more like adultery) exhibited by king David and Solomon. My partner and I of 7 years are committed 70-year old christians and this question does concern me.
I would suggest that you read 1 Corinthians 5. Its not important whether or not you can justify your decisions. That is what the Pharisees tried to do. Pray and ask the Lord to show you whether he is happy with the way in which you are living. Remember that we as Christians are requiered to be living examples of Christ so that the world may see and believe. I pray that He will reveal Himself to you in His Glory.
Now I am confused...when once upon a time there was no marriage "Papers" or ceremonies....just that the couple be known as husband and wife. When were marriage "papers" come on the scene? Many performances of marriage turn out to be a means for someone to gain money for this and is hardly ever performed freely, so I wonder what is REALLY the intention of introducing a "paper"? In the states of "common law" all one has to do is have a joint bank account and be known to others as husband and wife. So in that view, Christians obey the laws of the land in accordance to obeying God. And WHOSE opinion was this concept of only one acceptable way?
I think we are introducing other concepts not in question by the thread starter (TS) or original post (OP). That is, the situation presented are two people who are not married, who know they are doing wrong and do not intend to marry.
Whether marriage requires a piece of paper or some sort of ceremony, although interesting topics on their own, does not alter the OP question.
Howsoever you interpret a marriage, can they "be unmarried & sexually active & know they are in sin & not repent yet still go to Heaven?" That, to me, seems to be the question that was asked.
I actually agree that a marriage in God's sight is no more than a commitment of two people to become one flesh and not separate. Neither is there a question of sin as they say they know they are doing wrong. Nevertheless, my understanding of sexual immorality is sex for one's own selfish pleasure and/or with someone to whom you are not 'married.'
So the question to me can be paraphrased as, "if an uncommitted couple live together in sexual sin, can they still go to Heaven if they love each other consider themselves believers, are aware that they are hurting God but choose not to either refrain from the sin or commit?"
Depending on your belief on what marriage is, you may paraphrase differently.
So the interpretation of Marriage nor sexual sin is not in question for the TS.
Damian's comment is spot on. The church should get out of the marriage business as should the government. Marriage in Genisis consisted of a man going in to a woman. The Church should be in the marriage blessing mode as an act of expressing Christ's love. Scripture doesn't say anything about church weddings for Adam, Abraham, Isaac or Jacob. In committed fornication is clearly sinful behavior. Lack of a government issued license or pastor's/magistrate's signature on a contract for a committed man and woman does not make their union a sin.