Will all Israel be saved?

And in this way all Israel will be saved (Rom 11:26).

What Paul meant by that is hotly-contested. Any interpretation is probably inconclusive.

i) Some think it refers to the "new Israel": the community of messianic Jews and Gentiles Christians (e.g. Stanley Porter, O. Palmer Robertson). That's a defensible interpretation. 

ii) Some think it refers to an endtime restoration/ingathering of the Jewish people. A latter day revival. I incline to that view. In fact, the growing messianic movement may be a case in point. 

iii) Based on OT usage, I also think it's probably an idiomatic phrase for a representative sample of Jews. (ii) and (iii) aren't mutually exclusive. 

iv) Some think it refers to the universal salvation of the Jews. But given how the OT distinguishes the righteous remnant from apostate Jews, including oracles of eschatological judgment, as well as how the religious leaders turned on Jesus, it's hard to believe Paul thought that would all be erased. 

v) In Israel you can see devout Jews pray facing the Wailing Wall. With all due respect, I'm afraid that illustrates the vacuity of rabbinic Judaism. To pray in front of a wall, a retaining wall, a relic of the Second Temple. That's so retrograde.  

vi) In the course of church history, many Jews never rejected the historical Jesus. They never rejected the NT Jesus. Rather, they rejected the Roman Catholic Jesus or the Eastern Orthodox Jesus. For them, the church was the face of Jesus. So many Jews massacred by Catholics. In that sense, they never knew what they're rejecting.

What if God saved them? What if they are part of "all Israel"? I just throw that out therefore consideration, as a neglected interpretation of Rom 11:26. Prophetic fulfillment can be surprising.

vii) Having said that, I hasten to add that absent divine intercession, humans are born lost. It's not something we have, then lose. Rather, we're born apostates–unless God intervenes. 

That's a problem with asking, "What about those who never heard the Gospel, through no fault of their own?" That overlooks the condition they're in. The starting-point isn't mere lack of enlightenment, but alienation from the life of God (Eph 2:3; 4:17-19; Tit 3:3). The revelation of Christ exposes their latent animosity (Jn 3:19-20).