These God will reattach through faith in Christ only (
Romans 11).
You need to take another look at Romans 11.
25 For I do not want you, brethren, to be uninformed of this mystery—so that you will not be wise in your own estimation—that a partial hardening has happened to Israel until the fullness of the Gentiles has come in; 26 and so
all Israel will be saved; just as it is written,
that is NOT talking about some group of mixed Jewish and Gentile believers; that is talking about the Israel that are "enemies of the gospel." (v 28)
If your theology does not allow God to change their hearts (the entire nation) and bring them to faith in Messiah, then you need to change your theology.
Jer 31:31 “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.”