Even if one was to accept the premise that Christians are angels (which is a stretch), in order for that person to be a Christian, they have accepted Christs atonement.
So, unrepentant could only be referring to sin remaining in their life due to that person being a fallible human. Living in that state of unrepentance towards sin has been termed being carnal (example: 1 Cor 3:3). That sin may hinder their daily walk with the Lord, and stunt the growth in Christ, but even that sin was forgiven based upon the Lord's payment. That forgiveness was made eternally effective the moment the person became a Christian.
So, calling a carnal Christian a fallen (whether he should be termed angel or not) has no more than temporal meaning.
The upshot of all this is that neither the premise of calling a Christian an angel, nor the predicate of calling a carnal Christian fallen means anything substantial.