Do you realize that the Jews who were broken off who did not believe where born as jews? So yes they were broken off from the true vine as they did not believe. The OC was obsoleted, their is no OC anymore. But there cant be any gentiles broken off as they were never jews of the OC ways who had been having their sins forgiven by animal sacrifices, the ones who did live in the OC, also did have faith.
You cant escape this, Jews thought themselves the chosen ones of God, but they were broken ff because of unbelief in Christ, they never did believe when God made the transition in the NC.
But all those saved in the NC are eternally saved as they wont give up their faith if they were truly saved at all before.
If you view the being broken off as people groups, jews and gentiles, who do not believe, then the gentile nations who fall away due to apostasy could be considered being broken off due to the great apostasy that is coming and seems to be here today proceeding the revealing of the Antichrist figure.
I dont think your ever going to understand that God knows those who are His, they will remain faithful to the end, as He chose them from the beginning for salvation and they will persevere in faith, it is the P in the TULIP.
2 Thessalonians 2
13 But we are bound to give thanks to God always for you, brethren beloved by the Lord, because God from the beginning chose you for salvation through sanctification by the Spirit and belief in the truth, 14 to which He called you by our gospel, for the obtaining of the glory of our Lord Jesus Christ. 15 Therefore, brethren, stand fast and hold the traditions which you were taught, whether by word or our epistle.
16 Now may our Lord Jesus Christ Himself, and our God and Father, who has loved us and given us everlasting consolation and good hope by grace, 17 comfort your hearts and establish you in every good word and work.
God has given them everlasting consolation and good hope by grace, as they have been chosen by Him from the beginning (before the foundation of the earth, read Ephesians 1), for salvation through sanctification and belief in the truth.
And this NC established by Christ in His blood functions totally different than the OC with the Jews who had to offer continual sacrifices for their sins, and God did not write His laws into their hearts and minds so that they would know Him and not leave Him which many of the Jews did throughout their histories.
Hebrews 8
A New Covenant
7 For if that first covenant had been faultless, then no place would have been sought for a second. 8 Because finding fault with them, He says: “Behold, the days are coming, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah— 9 not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they did not continue in My covenant, and I disregarded them, says the Lord. 10
For this is the covenant that I will make with the house of Israel after those days, says the Lord: I will put My laws in their mind and write them on their hearts; and I will be their God, and they shall be My people. 11 None of them shall teach his neighbor, and none his brother, saying, ‘Know the Lord,’ for all shall know Me, from the least of them to the greatest of them. 12 For I will be merciful to their unrighteousness, and their sins and their lawless deeds I will remember no more.”
13 In that He says, “A new covenant,” He has made the first obsolete. Now what is becoming obsolete and growing old is ready to vanish away.
And besides all this, if your still reading, no one who is saved in the NC can sin, note v9.
1 John 3:8
He who
sins is of the devil, for the devil has
sinned from the beginning. For this purpose the Son of God was manifested, that He might destroy the works of the devil.
1 John 3:9
Whoever has been born of God does not
sin, for His seed remains in him; and he cannot
sin, because he has been born of God.
And if you don't know what this means, and pop up objections contrary to v9, I am not sure you are a New Creation in Christ, but I hope you are.