First, the Bible is only one of many holy scriptures in the world.

The Hindus have their scriptures too for instance which they regard as highly as Christians regard theirs. And there are many other traditions about what happens in the future.

For instance, as an example of another tradition, many Buddhists believe that the historical Buddha is the fourth of a series of a thousand Buddhas that arise from time to time, their teachings last for a few thousand years, then fade away and eventually after many thousands of years new teachings arise again.

So in those traditions, there are 996 Buddhas still to come in our world system, so got a fair while yet. This particular world system with its 1000 Buddhas is a part of larger and larger cycles ending with destruction indeed, and renewals, because nothing is permanent. But that's in the far distant future,maybe millions of years into the future. This is not a creed, not in Buddhism, but many Buddhists think this way just because that's how they were brought up (the numbers like 4 and 996 here vary depending on the tradition).

REVELATIONS ORIGINALLY WRITTEN AS A MESSAGE OF ENCOURAGEMENT AND HOPE FOR EARLY CHRISTIANS

Also, amongst Christians also, there's a wide range of views on how to interpret the Revelations (and related passages in the gospels), summarized in  "From Adam to Armageddon: A Survey of the Bible", page 178 as

"1. A view that Revelation must be understood in the context of its own time and the events symbolized in its pages as having already taken place.

"2. A view that only a portion of the revelations have occurred and that the work offers clues to the remaining portion of human history.

"3. A view that the book is best understood spiritually, and no attempt should be made to interpret it in the context of history.

"4. A view that the book is prophetic and its prophecies are yet to be completely fulfilled."

The idea of a literal Armageddon is the fourth of those common ways of interpreting the Bible.

Revelations was added to the Bible at quite a late date. It was originally regarded as heretical by some of the early Christians. There are passages related to it, in the gospels, such as  Matthew 24-25, which talk about events that it says would come to pass before the current generation passes away. Differences Between Matt 24, Mark 13, And Luke 21 - Gracethrufaith

Revelations originates as a message of hope to first century Christians who were being persecuted and many of them dying for their faith. As the author of "From Adam to Armageddon" says

"Regardless of whether Revelation holds the secret of the time and place that history as we know it will end, it holds the view that how one lives matters greatly. That alone makes  it of value for those who use it as an authority for their lives. Its vision may have been intended primarily to support Christians facing death for their first century faith, but it has served a much broader purpose for continuing Christianity. A book of comfort and devotion, it has called people to faithfulness over the years, while assuring them of the faithfulness of the God it proclaims."

(From Adam to Armageddon: A Survey of the Bible - page 180 )

That's why the view 1, that the events described in Revelations have already taken place is also a reasonable view to take, or the view 3, that it is best understood spiritually, in both cases it has no future predictive power since it either describes events of the first century AD, or it is meant to be taken spiritually, as a message of hope with no intention of prophecy of actual events in the world. And many Christians do take it in those ways.

MORE THAN 242 FAILED PREDICTIONS OVER THE LAST 2000 YEARS

And there are many failed predictions going right back to the time the Revelations were written. See this list of predictions of the end of the world. Also this list of 242 predictions of the end of the world.

If you are thinking about the idea of the giant asteroid impacts, blood Moons etc etc - the bible doesn't give any dates anyway, and doesn't say anything about giant asteroids. At that time nobody knew they existed.

Nobody knew where meteorites came from. Ideas for their origins included strong winds, thunderstorms and volcanoes.

Nobody knew that meteorites came from space until Ernst Friedrick Chladu published his theory in 1794 "On the origin of the Mass of Iron Discovered by Pallas and Others Similar to It, and on Some Natural Phenomena Related to Them". That was also before the discovery of Ceres in 1801, so nobody knew the asteroids existed either. So there is no way the Bible could predict the motions of asteroids.

While on the other hand the methods of astronomy and science lead to accurate and successful predictions of many astronomical events each year. Predicted often accurately to the minute and even the second.

This is circulating on Facebook at present as a kind of spoof of all these doomsday scenarios.

LITERAL ARMAGEDDON - NO REASON TO THINK IT IS MORE LIKELY NOW THAN IN THE FIRST CENTURY

Yes, the idea that there will be a literal Armageddon is a respectable view that some Christians hold as a matter of belief (one of many). However, I think there is no reason, even if you hold that belief to think it is particularly any more likely to happen now than it was in the century after Jesus died.

Not when you have that perspective of looking at that list of 242 predictions of the end of the world . Which is on going - that list doesn't include several new ones predicted since 2012, which didn't happen, with several failed predictions this year already.

And perhaps it helps to have a bit of perspective to realize that for many other traditions, such ideas have no hold on their minds at all. If you were brought up as a Hindu or Jain or Buddhist or Taoist or Shintoist or in a Shamanistic tradition or with Ancestor worship etc etc then these ideas would mean nothing to you.

And that there is also a wide range of views amongst Christians, so it could be interesting to know that there is this variety of views.

WORLD ENDING EVENTUALLY

As to why the world would end eventually - I think that it will become uninhabitable about 500 million years from now, unless we find a way to do something about it, as the sun heats up on the way to becoming a red giant.

And if we find a way past that - well won't be us anyway probably evolved into something else long before or extinct and new species and civilizations arise. But if so - well eventually something will happen eventually. End of the universe perhaps. Or just that parts of it become uninhabitable. Either way nothing lasts forever. But that doesn't make the universe and our Earth any less precious.

And I think teachings like this are surely meant to inspire us to look at our lives and treat them as more precious and of greater value and inspire us to live better and more meaningful lives. If you end up getting scared and upset - for no reason, especially repeatedly, for one predicted but failed Armageddon after another - I'm sure that can't be Jesus or God's message,if that is indeed what this book is. Whatever it means.

(I'm writing this as a Buddhist answering a Christian question, but I've got a reasonable background in Christianity / theology as well, my parents were both ordained ministers and also missionaries as well, I grew up surrounded by shelves and shelves of books on theology belonging to my father - and read lots of theology as a child  out of interest - so - just enough to suggest a few pointers towards other ways of looking at such questions, and felt it might be interesting to show that there are other perspectives on it.)