This is a good question Utah, because so many people misread the Bible on this point, many of them in this forum. They think that all Israel being saved means that everyone from a cultural Jewish background as a political nation on the map will be saved in some end times scenario. Not at all. They are misreading verses. Paul tells us who Israel is, even in the very same book of Romans: "For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh:". One reason for the error is a casual reading of these verses:"And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob: For this is my covenant unto them, when I shall take away their sins." The word "so" in this statement does not mean "then" as so many would-be theologians say. The word "so" means "in this manner, in this way". Go look it up in the concordance and you will see this. And what manner is that? Exactly as the chapter has been describing. In the manner of grace and not works. In the manner of a remnant of both cultural Jews and cultural Gentiles. If the word "so" meant "then", then we would read: and then all Israel will be saved. But instead we have to read: And in this manner will all Israel be saved. In the manner of being saved by grace. The Israel being spoken of is the Jew who is one inwardly. The verse is saying that the true believers (Israel means everyone who is a true believer from any background) will be saved in this manner. Not by THEN a whole cultural and political nation being saved. The verse then continues: "There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob: For this is my covenant unto them, when I shall take away their sins." This means that Jesus comes from heaven and turns people who are then true believers (Jacob is a parable word describing all true believers from any background) away from ungodliness to Christ. Then verse explains that this is God's new covenant in Christ, namely, that the deliverer (Christ) takes away people's sins. It is explaining that Jesus has already come from heaven and set up this new covenant.
Romans 11 explains in earlier verses that cultural Jews are not prevented from accepting Christ, else Paul, who was a cultural Jew would not be able to be saved. Rather, only a part of them is saved, not all of them. It is the same with the Gentiles. Paul warns Gentiles not to get puffed up and think that because they are cultural Gentiles, they are guaranteed salvation. He does not say that he will graft back all cultural Jews. He is merely warning Gentiles to consider what God is able to do.
People also base this notion of all cultural Israel suddenly being saved in an end-time scenario from verses from the Old Testament (which they see as prophecy about cultural Israel). What they are refusing to acknowledge is that these are prophecies pertaining to spiritual Israel. They do not understand that the Bible is written in parable form, as it is written: "Give ear, O my people, to my law: incline your ears to the words of my mouth. I will open my mouth in a parable". Again, it is written: "But without a parable spake he not unto them: and when they were alone, he expounded all things to his disciples." You can take their advice and their understanding but it will not be anything real.