If Israel is cut off as you say then this means God will not keep covenant, will not keep His promises to Abraham, Isaac, and Jacob, and the children of Jacob/Israel.
Take notice what the Word of God says here:
7 And I will establish my covenant between me and thee and thy seed after thee in their generations for an everlasting covenant, to be a God unto thee, and to thy seed after thee. Gen. 17:7.
Cut off does not mean "everlasting" and I'd rather receive what is written over your erroneous re-interpretation of the Scripture. Jesus said, "Scripture cannot be broken" and the Scripture He was referring to is the Hebrew Scripture of Law, Psalms, and Prophets. The same Hebrew Scripture the apostles including Saul taught the people from.
Christ promised to build His Church and He began building His Church on the Day of the Feast of Harvest (Pentecost) in which He saved three thousand Jews, and Acts 2:47 say Christ added to His Church daily such as should be saved and in the days, weeks, months and years to come more Jews were born-again and added to Christ's Church. For the next four decades until the Romans (Gentiles) destroyed Israel and the Jewish Temple Jews were being baptized into the body of Christ by the thousands.
But before the birth of Christ where are Gentiles? Were they claiming to be in the Abrahamic Covenant? Even when Jesus walked the Holy Land where are Gentiles claiming Jesus as Lord? Where are Gentiles being sprinkled by the blood of the animal sacrifice slain for the sins of the children of Israel? The fact is NO GENTILES were ever claiming to be in the Abrahamic Covenant and the reason is because the covenants were between God and the Hebrew people. It was only AFTER the destruction of the Jewish Temple and the scattering of Jews into Gentile lands that Gentiles stole everything God gave to the Hebrew people through covenant and prophecy. Gentiles only began to steal Israel's inheritance AFTER Israel was scattered and their Temple destroyed.
Scripture cannot be broken. This means that anything that is written in the gospels or in the letters by Saul, Peter, John, James, IF what they say contradicts what is written in the Law, Psalms, and Prophets is to be rejected as a lie and there are many lies put forth by Gentiles since the destruction of the Jewish Temple. Gentiles are guilty of Inheritance theft, and they do it by interpreting Saul's letters, Peter's letter, John's letters, etc., that places those interpretations against the Law, Psalms, and the Prophets. THESE are the Scripture that CANNOT be broken (and they will never do that.) God controls everything. He will not allow anyone to manipulate, add, change, subtract His Word of Truth.