I would ask if one is justified how does it at that very moment depend on what one will do in the future? I would propose that if you have been moved to repentance and have been given the gift of true faith that when you call upon the Lord for salvation you are 100% justified at that moment.
The New Covenant
31 "Behold, days are coming,” declares the Lord, "when I will make a new covenant with the house of Israel and with the house of Judah,
32 not like the covenant which I made with their fathers in the day I took them by the hand to bring them out of the land of Egypt, My covenant which they broke, although I was a husband to them,” declares the Lord.
33 "But this is the covenant which I will make with the house of Israel after those days,” declares the Lord, "I will put My law within them and on their heart I will write it; and I will be their God, and they shall be My people.
34 They will not teach again, each man his neighbor and each man his brother, saying, ‘Know the Lord,’ for they will all know Me, from the least of them to the greatest of them,” declares the Lord, "for I will forgive their iniquity, and their sin I will remember no more.”
35 Thus says the Lord,
Who gives the sun for light by day
And the fixed order of the moon and the stars for light by night, Who stirs up the sea so that its waves roar;
The Lord of hosts is His name:
36 "If this fixed order departs
From before Me,” declares the Lord,
"Then the offspring of Israel also will cease
From being a nation before Me forever.”
37 Thus says the Lord,
"If the heavens above can be measured
And the foundations of the earth searched out below,
Then I will also cast off all the offspring of Israel
For all that they have done,” declares the Lord.
docs: These verses include, "I will never cast Israel off for what they have done" etc. is presented in the context of the arrival of a new and better covenant (the law written in their minds and hearts. If God promises never to forsake or cast off Israel even when they sin then why isn't the same true for us believers who have been justified by the blood of Israel's Messiah? The weakness of men and their flesh cannot nullify the promises of the new covenant. If God will be this faithful to Israel then why not His church? If you are truly justified you are going to make it. It does not seem to depend on "if" but rather God's faithfulness to you such as He has always expressed to the believing remnant of Israel. If that is true for them then why not us? Being honest, I've never known many truly born again people who have turned away. A very few here and there. Perhaps their fate remains a mystery to a degree but is there such a thing as being "unjustified?" Our understanding of the new covenant and the power of justification should maybe be based not so much on avoiding the conditional "if" but concentrating on God's faithfulness best typified by His dealings with Israel and the lasting power of justification seen in New Testament saints who believe.
I'm eating a snack and sitting here. I don't have all the answers and talk too much. But I love talking about these things because there is much to learn from every angle even if we disagree a bit. Justification from God is the real deal. I know you know this.
Blessings.