I fail to understand how the fact the Jews (natural branches) will be regrafted into the natural olive means that wild branches (gentiles) that are cut off after being grafted in can be grafted back into the natural olive. Paul quotes from Isaiah 59 to make his point:
Isaiah 59:20-21
20 "And a Redeemer will come to Zion,
And to those who turn from transgression in Jacob," declares the LORD.
21 "And as for Me, this is My covenant with them," says the LORD: "My Spirit which is upon you, and My words which I have put in your mouth, shall not depart from your mouth, nor from the mouth of your offspring, nor from the mouth of your offspring's offspring," says the LORD, "from now and forever."
NAS
The 144,000 will evangelize the Jews and after the Lord returns all the Jews will be gathered in the Promised Land. God has not revoked His covenant with Abraham.