+Vijay S Mane
and anyone else interested. I'm not sure if you are asking what the "traditional" Christian belief is, or my personal opinion as to what will happen. But I'll center on what the various traditions have been over time.
First off - this concern with the end of world is largely referred to as "eschatology" . and it is a belief that is not exclusive to Christianity. All the major religions have some version of the "end of all things" story. A non-Christian example, Ancient Norse religion's day called "Ragnarok" where not only the entire universe is destroyed but also all the Gods and from the debris of the last day springs up a new order of Gods and a new universe.
For Israelites in the First Century BCE, there was an overwhelming sense of bitterness. They had repeatedly been conquered, exiled or occupied. First by the Assyrians, then the Babylonians, the Persians - who weren't as bad and allowed them to return to Israel - then the Greeks, who tried to Hellenize the entire country. They had a brief respite for a little over a century after the revolt of the Maccabees but then came the Romans and that was all she wrote - Ancient Israel would no longer be a free and automonous country.
The Israelites believed that there was only one true living God ("living" essentially means he was not an idol carved in stone or "dead". A better description for a modern audience would "real" vs. "pretend") . A problem arose for the Israelites when they considered if they were the "chosen" people and their God was the one and only true God - why the heck are they getting conquered all the time? Will there be no respite? "We are following God's law all the time, but still, we are being punished while others who are evil are being awarded in life? Why does God allow this to happen?"
There are a number of simple answers to this question. God doesn't exist and we've just been fooling ourselves all this time. God exists but he's not as mighty as we first thought. Or, God isn't alone - there are other gods out there and either our God is puny by comparison or they have united in stopping him from protecting us.
But, no. The Israelites came up with something far more elaborate. I can't recall the psychological term but it is similar to the effect of an abused child. "Daddy loves me but also daddy hurts me." so the child's imagination comes into play - the devil possesses daddy when he beats me. A full cultural disconnect arose within the Israelite community, influenced by Zoroastrianism - God is not responsible for the evil in the world and our suffering. The devil and wickedness are in control, that's why we suffer. And why? It's all part of God's elaborate plan. God is giving the wicked free reign so that they compound their sins to the point where it would be nearly be impossible for them to redeem and when they have reached the ulimate point of depravity - God will come and conquer the wicked world and remake it into a kingdom of goodness. All the former rulers will be thrown into eternal punishment in hell. And so on . . .
What this closely resembles is the scrawny, defenseless kid being beaten and swearing to his abusers, "Just you wait - when my daddy gets home, he'll beat you far worse than you're beating . . .just you wait, then you'll see. And, boy, will you be sorry then" - because in both scenarios - the victim is absolutely helpless, sure the Israelites had their moments of success against the Romans, but ultimately - they were fated to lose because the Romans had better technology, better weapons and were absolutely ruthless. This was what the Israelites held onto so as never to admit full defeat.
Now - this is the state of Israel when Yeshua of Nazareth comes into the world. And besides himself, there are a number of "prophets" or "teachers" spinning this story. They are known to scholars as the Apocalyptic Prophets - all with the same one main theme - the end of the world is coming, all will be reversed, evil will be punished and you must repent and follow God's laws. It is common throughout the land. Near the Dead Sea at Qumran - a group known as the Essenes are living in a monastic community specifically to prepare for this coming "end of days". And in the North in Gallilea - Yohanan the Baptist - was teaching the same message. This message was passed downto his disciple -Yeshua of Nazareth who continued to spread it with his own additions and customizations to the story -
I don't want to get into the particulars but - I will point you to the following -
Καὶ ἔλεγεν αὐτοῖς· Ἀμὴν λέγω ὑμῖν ὅτι εἰσί τινες ὧδε τῶν ἑστηκότων, οἵτινες οὐ μὴ γεύσωνται θανάτου ἕως ἂν ἴδωσι τὴν βασιλείαν τοῦ Θεοῦ ἐληλυθυῖαν ἐν δυνάμει.
And he said to them, "Certainly I say to you that there are some of those here standing, who will not taste death anyhow, until they see the kingdom of God in power.
This statement is largely believed to have been said by Yeshua of Nazareth - first, clearly it is an incorrect statement, all those standing there at that time are now dead. It is unlikely that an obviously false would be created and attributed to Yeshua by later Christians since it would serve their purpose to show him as being blatantly incorrect. It's most likely still preserved in the gospel due to having some weight of authenticity.
What this means is that Yeshua of Nazareth believed that the end of days was coming WITHIN HIS DISCIPLES LIFETIMES. I.e. the first century CE.
Consider Mark 13:30
ἀμὴν λέγω ὑμῖν ὅτι οὐ μὴ παρέλθῃ ἡ γενεὰ αὕτη μέχρις οὗ πάντα ταῦτα γένηται.
Certainly I say to you that no one of this generation will have passed away until all these things shall have taken place.
Well -it didn't happen.
Move to Paul - also believed that the end of days would happen within his lifetime. consider the letter to the Thessolonians -the earliest writing by Paul
τοῦτο γὰρ ὑμῖν λέγομεν ἐν λόγῳ κυρίου, ὅτι ἡμεῖς οἱ ζῶντες οἱ περιλειπόμενοι εἰς τὴν παρουσίαν τοῦ κυρίου οὐ μὴ φθάσωμεν τοὺς κοιμηθέντας· 16 ὅτι αὐτὸς ὁ κύριος ἐν κελεύσματι, ἐν φωνῇ ἀρχαγγέλου καὶ ἐν σάλπιγγι θεοῦ, καταβήσεται ἀπ’ οὐρανοῦ, καὶ οἱ νεκροὶ ἐν Χριστῷ ἀναστήσονται πρῶτον, 17 ἔπειτα ἡμεῖς οἱ ζῶντες οἱ περιλειπόμενοι ἅμα σὺν αὐτοῖς ἁρπαγησόμεθα ἐν νεφέλαις εἰς ἀπάντησιν τοῦ κυρίου εἰς ἀέρα· καὶ οὕτως πάντοτε σὺν κυρίῳ ἐσόμεθα.
For this we say onto you in the Word of the master, that of us living, remaining for the coming of the master, will not precede those already dead. For the master himself shall descend down, in an archangels shout and the trumpet of God, and the dead in Christos shall rise first. Then we living, we remaining, being captured in the clouds, to meet the master above in the air and so shall we ever remain with the master.
(Note: I treat Kurios as "master" and not Lord since the word "Lord" has a different modern connotation that was used in ancient times.)
Paul is making a distinction - using "we" for those living and "those" for those dead. "We" is first person plural, it includes Paul. Paul believes he will be alive at "end of days"
But as time passes - as more disciples and followers die - the story changes.
I'll continue later.