Those literal Israelites who don’t believe WILL NOT BE GRAFTED BACK IN, EVER. Disobedience and unbelief have sealed their fate. God did not spare the natural branches because of unbelief and the same applies to Gentiles.
Romans 11:
11I say then, Have they stumbled that they should fall? God forbid: but rather through their fall salvation is come unto the Gentiles, for to provoke them to jealousy. 12Now if the fall of them be the riches of the world, and the diminishing of them the riches of the Gentiles; how much more their fulness? 13For I speak to you Gentiles, inasmuch as I am the apostle of the Gentiles, I magnify mine office: 14If by any means I may provoke to emulation them which are my flesh, and might save some of them. 15For if the casting away of them be the reconciling of the world, what shall the receiving of them be, but life from the dead? 16For if the firstfruit be holy, the lump is also holy: and if the root be holy, so are the branches.
17And if some of the branches be broken off, and thou, being a wild olive tree, wert graffed in among them, and with them partakest of the root and fatness of the olive tree; 18Boast not against the branches. But if thou boast, thou bearest not the root, but the root thee. 19Thou wilt say then, The branches were broken off, that I might be graffed in. 20Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear: 21For if God spared not the natural branches, take heed lest he also spare not thee. 22Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in his goodness: otherwise thou also shalt be cut off. 23And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again. 24For if thou wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be graffed into their own olive tree?
25For I would not, brethren, that ye should be ignorant of this mystery.... l
Yes, that is true.