I was listening to a conversation between two people describing the situation of a new believer, a woman with many physical problems and high medical bills. The woman has been living with the father of her children for 30 years. They are not married because his insurance would never accept her, so in order to receive these benefits they are not married. One person in the conversation suggested that she and her mate could be married in the church without a legal marriage license, so at least they wouldn't be living in sin. (We do not live in a common law state.)
I read your post about the existing authorities being sanctioned by God and I agree. Personally I believe that being married legally is the right thing and then trusting God to make a way through the medical bills is necessary. But how do you answer so many who find themselves in this situation?
"And why not say, "Let us do evil that good may come"? --as we are slanderously reported and as some affirm that we say. Their condemnation is just" (Romans 3:8).
What I commonly find in these types of situations is apparent conflicts that are of the person's own making. A lack of financial benefits is no excuse for fornication. Somehow I suspect that the woman's medical problems are not 30 years long since she had children. More likely she currently has severe medical problems and that is her current reason for not getting married as she should have done 30 years ago. Thus, her problem was manufactured by herself.
Currently, the issue is non-existent anyway. The government changed their rules so that pre-existing conditions cannot prevent a person from getting coverage. Therefore, she is either ignorant of the situation or being dishonest about her excuse.
But let's just suppose that she could not get married because it really would have created an impossible financial situation. (I would be skeptical that such could really exist. As you said, things have a way of working out when a person is determined to do what is right.) Even then, it doesn't mean she could have sex without being married. It would only mean that she denied herself the privilege of a husband because something else -- money -- was more important to her.
Also, poor decisions in the past do not excused continued poor decisions. "What shall we say then? Shall we continue in sin that grace may abound? Certainly not! How shall we who died to sin live any longer in it?" (Romans 6:1-2). There is only one answer she has to end her sin; either by getting married or by moving out on her own. Continued sinning is never an option.