We've all heard that during the plague of darkness in Egypt, directly preceding the redemption, at least four-fifths of the Jewish people perished. We have also heard that the final redemption will parallel the redemption from Egypt, thus leading us to conclude that at least four-fifths of our people will Chas V'shalom not make it to see the final redemption.
I have substantial evidence that shows that this will not be the case, and I would like to present it as both hope and a prayer that indeed all of our people merit to see the final redemption, speedily and in our days.
The most obvious and explicit statement of this was made by Rebbe Nachman. He makes it very clear that there was a fundamental difference between the redemption from Egypt and the final redemption. He explains that there was a factor in the Exodus of speed. It was this speed that was what caused the Jews to leave with haste, not leaving time for their dough to rise (see Exodus 12:39). It was also this speed, says Rebbe Nachman, that prevented four-fifths of our people from leaving Egypt. There just wasn't time to wait for the Spiritual slumberers to awaken. Unfortunately they had to pass away. (This could be because the Jews were then teetering on the edge of the 49th level of impurity, and any moment more that they would remain in Egypt would have caused the destruction of the entire Jewish nation, Heaven forbid.)
Rebbe Nachman says that the final redemption WILL NOT HAVE THAT SAME ASPECT. It may be true that the final redemption will happen quickly, but it will not be the required haste as was necessary when the Jews left Egypt. This will ensure that all Jews will be redeemed b'ezras Hashem.
A second source for this which is older, but not as explicit, is a medrash I heard quoted by Rav Kessin. It relays a conversation between Moshiach ben Yosef and Hashem. Moshiach ben Yosef has become aware of the possibility that many of the Jewish people will not make it through to the times of Moshiach. This upsets him greatly and he declares his readiness to do whatever it takes so that they should survive. Hashem responds and says that in order to save them, he will have to descend to the depths of impurity in order to save every last soul, as many of them will be entrenched in evil. He agrees to this, and as he is sent down into the spiritual abyss, Moshiach ben Yosef screams in horror at the depths of the depravity he encounters, but nevertheless does accomplish his goal.
One could explain this medrash that it is speaking on a spiritual level, and that Moshiach is saving these Jewish souls from spiritual destruction. However, when one understands the role of Moshiach ben Yosef, it then becomes apparent what is being spoken of. Moshiach ben Yosef's job is the physical restoration of the Jewish people (similar to his forebear Yosef who provided physical sustenance to the Jews when they first came down to Egypt). Thus Moshiach ben Yosef's job includes bringing the Jews back to Israel, rebuilding the land, and even building the physical edifice of the third Beis Hamikdash (temple) itself. The role of Moshiach ben Dovid, on the other hand, is to bring the spiritual side into these physical constructs - the spirit back to the people, the holiness back to the land, and the Shechinah back to the Beis Hamikdash.
With this in mind, it becomes clear that when Moshiach ben Yosef is asking to save every last Jew, he is not just speaking about their spiritual existence, but rather, he is speaking about their physical existence as well.
Well, if this is true, you ask, why do we keep hearing that even during the final redemption many of our people will be lost, Heaven forbid?
I think the answer goes back to an argument we find in the Gemara in Rosh Hashana on pages 16b-17a.
The gemara there speaks of the Final Judgment that will take place and says that there are three groups on the Day of Judgment (similar to Rosh Hashana). A group of righteous individuals, wicked individuals, and middle of the road individuals. All agree that the righteous are immediately written and sealed for [Eternal] Life. The wicked are sentenced to Hell.
Here's where it gets interesting. What is with the 'middle of the road' class? So, in regards to Rosh Hashana, the gemara says that their judgment is suspended while they have ten days to do Teshuva (repentance). But in the final judgment, there doesn't seem to be a period of grace.
Beis Shamai says that these people are sent down to Hell [where they are purified], and then they float up. This is based on the verse (Zechariah 13), "And I will bring the third group through fire, and I will purify them as silver is purified [of its impurities], and I will check them as one who checks gold [for impurities]. He will call in My Name, and I will answer him." About this group did Chana say (I Shmuel 2), "Hashem kills and gives life, brings down to the depths [of Hell] and raises."
Doesn't sound too good, does it? Don't be too scared yet, because Beis Hillel argues.
Beis Hillel says that with regards to this group, ורב חסד מטה כלפי חסד - the One who is abundantly kind leans toward Kindness [i.e. Hashem shows kindness to the middle group, and does not send them into Hell.] About them did King David say (Psalms 116), "I love when Hashem hears my voice," as well as the rest of that parsha, including, "I was bereft, and He saved me." (These are the verses from Hallel - אהבתי כי ישמע ה' את קולי... דלותי ולי יהושיע)
It seems to me that Beis Shamai and Beis Hillel are arguing about our four-fifths of the Jewish people, and Beis Shamai says that they will have to do some time in Hell, whereas Beis Hillel says that there will be an overwhelming Kindness that Hashem will show His people.
Amazingly, the gemara there explains the verse דלותי ולי יהושיע, I was bereft, and He saved me - as meaning that despite the fact THAT I WAS BEREFT OF MITZVOS, to You [Hashem] it is beautiful to save me! Is there a clearer description of our four-fifths than that?
But what of Beis Shamai who says that the middle-of-the-road class of people don't make it? The answer is that the halacha is like Beis Hillel until Moshiach comes. Only when Moshiach comes do we go in accordance with the views of Beis Shamai. Since the judgment we are talking about is occurring BEFORE Moshiach, it is clear that this four-fifths of the Jewish people will survive in accordance with Beis Hillel's ruling!
This also explains why the autistic individuals are saying that there will be such mayhem and destruction before Moshiach chas v'shalom - because they are 'living in the world of truth!' In their world, all they see is a world of Din (pure judgment) and thus they see the ruling of Beis Shamai. We, however, who live in a world mixed with Din and Rachamim (mercy) will experience a reality based on the ruling of Beis Hillel - All of our people will survive, bezras Hashem, except for the most wicked individuals.
This leaves us with a small quandary. Based on what I am saying, why should we bother to do Teshuva? In any event Hashem will have mercy on us and redeem all of His people!
The answer is based on something that Rabbi Akiva Tatz writes in his book Living Inspired. While it's true that G-d willing, all of our people will survive, there will be a tremendous level of embarrassment that will be endured, Heaven forbid, when the truth of the spiritual world becomes evident. At that moment of truth, the contrast between Reality and how lives have been led will be most telling. For those who have lived their lives in accordance with the teachings of the Torah, their lives will reflect a harmony that will be exhilarating. For those who did not, however, their will be a tremendous dissonance that will result in a tremendous feeling of shame.
It is for this reason that we must redouble our efforts to do Teshuva, to try our best to constantly bring our lives in line with the dictates of the Torah - the Will of Hashem. We must develop our love of Hashem and our commitment to Him, and we must also pray on behalf of all our brethren who have not been privileged to know the Truth that they too should be drawn toward the light. The more we do this the more we will fulfill that which we say, "למען לא נבוש ולא נכלם" - in order that we not be embarrassed and mortified. The more we live a life of consonance with Truth, the greater will be our ability to fulfill the verse that speaks of the ultimate joy of Moshiach, "אז ימלא שחוק פינו ולשוננו רינה" - then will our mouths be filled with laughter, and our tongues with praise. May it be speedily in our days.