Although Jesus foretold that believers would lose their lives (see 24:9) not all apparently will, because He promised that those who endure to the end will be saved (see 24:13). That is, if they don’t allow themselves to be deceived by the false Christs or false prophets and resist the temptation to abandon their faith and fall away, they will be saved, or rescued, by Christ when He comes back to gather them in the sky. This future time of tribulation and rescue was also succinctly revealed to the prophet Daniel, who was foretold,
And there will be a time of distress such as never occurred since there was a nation until that time; and at that time your people, everyone who is found written in the book, will be rescued. And many of those who sleep in the dust of the ground will awake, these to everlasting life” (Dan. 12:1-2).
Salvation will still be graciously offered even during those days, as Jesus promised that the gospel would be proclaimed to all the nations (literally, “ethnic groups and tribes”), giving one final opportunity to repent, and then the end would come. It is interesting that we read in the book of Revelation what could very well be the fulfillment of Jesus’ promise:
And I saw another angel flying in midheaven, having an eternal gospel to preach to those who live on the earth, and to every nation and tribe and tongue and people; and he said with a loud voice, “Fear God, and give Him glory, because the hour of His judgment has come; and worship Him who made the heaven and the earth and sea and springs of waters” (Rev. 14:6-7, emphasis added).
It is thought by some that the reason an angel will proclaim the gospel then is because by that time in the seven-year tribulation, the Rapture will have occurred and all the believers will be gone. But that is, of course, speculative.
 This promise is often pulled from its context, and it is frequently said that before Jesus will return, we must complete the task of world evangelism. But within its context, this promise is speaking of a final proclamation of the gospel to the entire world just before the end.