For the most part, those I have run across that insist that only fellowship is severed rather than relationship, tend to believe that fellowship is temporary whereas relationship is permanent.
Example: In the parable of the prodigal son, fellowship was broken, not relationship.
Fellowship - koinōnia
To me this word speaks of relationship.
Communion.
JLB
The prodigal son parable is an interesting parable.
It appears to be written with the perspective of a believing family, out of which a son wishes to depart to discover life, and live it to the full.
Some have suggested this is the view of a believer who backslides and goes off into the world. They are still a son, but in the world, ie still alive in God, but carnal.
This is strange as the very parable as the prodigal son returns, the father comes and meets him on the road,
"this son of mine was dead, and is alive again – he was lost and is found!"
Luke 15:24
To be dead, is like you are no more, to be lost, is to be doomed to judgement.
There is hope to restore the relationship with God, no matter how far one has strayed, but there is no security if one has chosen to break the relationship permanently.
The attitude of returning son was repentant,
18 Father, I have sinned against heaven and against you.
19 I am no longer worthy to be called your son; treat me like one of your hired workers
Luke 15:18-19
In a sense when we are born we know the testimony of love to our hearts and God the creator yet we turn our faces against this and chart a course to make something of our lives.
Some want this story to be we are always safe, always a son, never lost, never dead to the Father. But the profound reality is the prodigal son chose freely to get their inheritance and choose the road of indulgence, partying and revelry. This is very much the road Israel took as testified by the prophets, skilled in drinking games, but full of sin and shame. But it ended in the ditch, in failure, judgement and suffering. But the wages and house of the King is consistent, real, permanent and dependable.
A simple choice, die in the way of the world, or return to the house of the King, and restore the fellowship our hearts desire.