Russell anticipated the return of Israel in his day. It was Rutherford who "spiritualized" the many prophecies and scriptures that foretold the restoration of Israel by applying them to "spiritual Israel." But this would not make sense particularly in view of Paul's discussion in Romans, chapters 9, 10, 11. He quotes prophecies from the O.T. that apply to fleshly Israel. Just after mentioning "all Israel" he quotes from Isaiah: "The deliverer will come from Zion, he will turn godlessness away from Jacob. And this is my covenant with them when I take away their sins." Paul concludes "For God has bound allmen over to disobedience so that he may have mercy on them all."
While "all Israel" may include those Gentiles who become spiritual Israelites because of their faith, it also has to include fleshly Israel just as the original prophecies indicated.