In what sense will "all Israel" be saved in Romans 11:26? Does this refer to the church and the inclusion of both Jew and Gentile (vs. 25; cf. Acts 15:6-11; Gal. 6:15-16)?
In Romans 11, Paul addresses the question that he sets forth in verse 1. "Has God cast away his people?" It was a question that was being asked by some Gentile Christians (vs.13) because Paul was preaching the gospel to them instead of the Jews as was his habit to do, after he first approached the Jews with the gospel (cf. Acts 13:46).
One key verse of the passage is in verse 7, "What then? Israel hath not obtained that which he seeketh for; but the election hath obtained it, and the rest were blinded...." Israel, as a nation, had not accepted Jesus as the Messiah. Some, however, did accept Jesus as the Messiah. Those who accepted Him were saved; those who did not fell (vs.11, 12) and through their fall, grace came to the Gentiles.
Does this mean that they cannot be saved? No, in fact, Paul wanted them to be saved. He was preaching to the Gentiles partially to provoke the Jews into accepting salvation (vs.14). Paul then gives us the Allegory of the Olive Tree. In this allegory, it is those who are grafted into the tree that are saved. The Jews are represented as the natural branches, but which had been broken off due to their rejection of the gospel. The Gentiles are represented as those who were grafted in due to their acceptance of the gospel. Toward the end of the allegory, however, Paul discusses those Jews who had first been broken off and what would happen to them if they accepted the gospel. He says, "And they also, if they abide not still in unbelief, shall be graffed in: for God is able to graff them in again" (vs.23). Notice, "IF they abide not still in unbelief." They have to become believers to be grafted back into the tree.
Verse 26 of Romans 11 is a conclusion to the allegory. Notice that Paul says, "And SO all Israel shall be saved." Paul doesn't say, "all Israel shall be saved," but "SO all Israel shall be saved." The word "so" is an adverb of manner. It means in such a way, or in such a manner, all Israel shall be saved. The idea is that they will be saved in the same manner in which they are grafted back into the Olive Tree, through belief that Jesus is the Messiah.
The covenant that God has with Israel now is the same that He has with the whole world. It is the covenant in which sins are taken away (vs.27). We need but look in Hebrews 10:16, 17 to understand this: "This is the covenant that I will make with them after those days, saith the Lord, I will put my laws into their hearts, and in their minds will I write them; And their sins and iniquities will I remember no more." What is this covenant? It is the new covenant; the first covenant has been taken away, that the second could be established (Hebrews 10:9).
Verse 26 concludes Paul's reasoning: "For God hath concluded them all in unbelief, that he might have mercy upon all." Now, both Jews and Gentiles are saved through the same method--the mercy of God.
Today, God is no respector of persons (Acts 10:34, 35). All are saved in the same way, through belief in the gospel of Christ, both Jew and Gentile. To answer your question, yes, this refers to the salvation that is afforded in Christ, through the church (Ephesians 3:23).