The last days is an expression found in the Bible. Generally, it refers to an epoch in human history wherein entropy and chaos will increase until the end. A man studying the Scriptures during the 1st or 2nd century could have correctly concluded that he was living in the last days. However, a woman who studies Scripture during the 20th or 21st century would also be correct in reaching the same conclusion. The last two completed centuries (1800-1999) witnessed an intensification of events that are aligned with the doomsday prophecies. As of this writing, we are surely living within the last days, although the 7-year Holokaustos may or may not begin within our lifetime. Thus, the last days are closely associated with the Holokaustos and the Revelation judgments.
In other words, the last days is a long period of history that climaxes with the 7 years of holokaustos described in the Book of Revelation. If none of the people alive today (as of this writing) were to live to see the Holokaustos, then this is what we may call a good problem to have. Such a hypothetical would place the beginning of the Holokaustos around the middle of the 22nd century. However, it is more important that people seek salvation through faith in Jesus Christ now, regardless of where (or when) exactly we are situated within history. This has been the case for unknowable billions of Christian believers.
Luke 21:36 encourages believers to pray that they may escape all these things. Today, there are hundreds of millions of Christians in Heaven who did not go through the holokaustos. Had they prayed per Luke 21:36 during the thousands of years that were not the time immediately preceding the end, it is plausible that Jesus Christ could have answered those prayers by sparing them from suffering during their time.
It is also unclear why Jesus Christ would tell Christians to pray in this manner, if in fact they were already pre-determined to suffer through the holokaustos and judgements of Revelation regardless of their prayer life. This is a question that post-tribulation believers have difficulty in answering.
Luke 21:36 Watch ye therefore, and pray always, that ye may be accounted worthy to escape all these things that shall come to pass, and to stand before the Son of man.