Of course Protestantism is a large field. But I was taking Wesley as typical of todays non-Calvinists. In his work on Perseverence,
http://evangelicalarminians.org/wp-content/uploads/2013/03/John-Wesley-Perseverance.pdf, he maintains that it is possible to make shipwreck of the faith. But he considers this to be, as I said in the previous posting, a definitive rejection of the faith. He quotes 1 Tim 1:18, and concludes
(1.) These men (such as Hymeneus and Alexander) had once the faith that purifies the heart, that produces a good conscience; which they once had, or they could not have put it away.
(2.) They made shipwreck of the faith, which necessarily implies the total and final loss of it. For a vessel once wrecked can never be recovered. It is totally and finally lost.
Im not going to assert that its absolutely impossible for such people to come back to faith, but Arminians commonly quote passages such as Heb 6:6, which doesnt leave much hope. This is not the kind of sin into which David fell, from which he repented.
So Im trying to make a distinction between a follower of Christ who sins, even seriously and someone who abandons the faith entirely. I believe justification continues despite sin, even serious sin. Thats the whole point of Luthers concept of justification, and its distinction from the Catholic definition. People dont fall into and out of justification as they sin and repent. Now continuing, unrepentant sin may very well be part of the process of making shipwreck of the faith, if you believe this is possible. (Calvinists dont, of course.)But the classification of sins into venal and mortal, with mortal sins being so serious that they break justification, is quite contrary to common Protestant teaching.
I looked up the quotation from The Smalcald Articles. Its there.The context is certain people who said that sin didnt matter. I would agree that sin matters, and that it changes how God works with us. However if the statement there implies that David lost justification (something it doesnt actually say), it would not seem to be consistent with Luthers basic concept of justification. David certainly sinned very seriously. He was called to account, and repented. I dont believe he stopped being justified during that period, nor that God, including the Holy Spirit, abandoned him. However the way in which God interacted with him certainly changed. Perhaps thats what the statement means. But God stuck with him, and brought him to repentance through the actions of the prophet. As far as I know, this analysis is not peculiar to Calvinism.
While you may not intend your use of state of grace to indicate something infused, the way you speak of it only make sense with infused grace.
For some quotations from Luther, see
What is "Mortal" Sin? - The Wittenberg Trail. My understanding of that is that he is not saying that certain sins are by nature mortal while others are not, but rather is making a distinction between a Christian, who is a servant of Christ even though he may sin seriously, and someone who is a servant of the flesh, who has made shipwreck of the faith (or wasn't one of the faithful in the first place). I would consider David to be an example of the first, and in fact an illustrative example of just how far sin can go in someone who is justified.