You are correct that Paul said the gospel had been preached in all the world (which was the Roman Empire in those days.) Paul said it in several different ways, showing the fulfillment of the prophecy of Matthew 24:14 relating to the destruction of Jerusalem, as well as the fulfillment to preach the gospel to "every creature" as instructed in Mark 16:15. [see Rom 1:8; Rom 10:17-18; Col 1:5-6; and Col 1:23]
But there was never any mention that it should be discontinued after that fulfillment, that I am aware of. Therefore, Paul continued preaching the gospel until Nero beheaded him. Peter and James also continued preaching until they were killed.
Paul also said this:
"Unto him be glory in the church by Christ Jesus throughout all ages, world without end. Amen." (Eph 3:21 KJV)
"Husbands, love your wives, even as Christ also loved the church, and gave himself for it;" (Eph 5:25 KJV)
That doesn't sound like a Plan B, or that the Church is going away, does it?
While it is true that most in Israel, and especially the leadership in Jerusalem, rejected Christ; it is also true that the Lord rejected them:
"But thou shalt say unto them, This is a nation that obeyeth not the voice of the Lord their God, nor receiveth correction: truth is perished, and is cut off from their mouth. Cut off thine hair, O Jerusalem, and cast it away, and take up a lamentation on high places; for the Lord hath rejected and forsaken the generation of his wrath. For the children of Judah have done evil in my sight, saith the Lord: they have set their abominations in the house which is called by my name, to pollute it. And they have built the high places of Tophet, which is in the valley of the son of Hinnom, to burn their sons and their daughters in the fire; which I commanded them not, neither came it into my heart. Therefore, behold, the days come, saith the Lord, that it shall no more be called Tophet, nor the valley of the son of Hinnom, but the valley of slaughter: for they shall bury in Tophet, till there be no place. And the carcases of this people shall be meat for the fowls of the heaven, and for the beasts of the earth; and none shall fray them away. Then will I cause to cease from the cities of Judah, and from the streets of Jerusalem, the voice of mirth, and the voice of gladness, the voice of the bridegroom, and the voice of the bride: for the land shall be desolate." (Jer 7:28-34 KJV)
Not only did the Lord reject Jerusalem and the cities of Judah, but those last two sentences sound a lot like the Lord was speaking of Babylon the Great, doesn't it.
Philip
So the Parthian Empire doesn't count? What of the Indian subcontinent and all of Asia (which were known)? What of the African coasts (which were known)? What opf the Celtic Barbarians?
You're skirting the issue ... the 'end of the age' was not before they were killed ... it was in 70 AD.
According to your view, the apostles (who were given the Great Commission) were resurrected at the 'end of the age' ... which you view as 70 AD via Matt 24:3. Since the Great Commission in Matt 28:20 would also continue until the end of the age ... logic dictates the conclusion that the Great Commission was fulfilled by 70 AD as well ... since the 'preaching of the gospel to the whole world' was completed before 70 AD ... when 'the end' of Matt. 24 came.
You either have a glaring inconsistency in your view (highlighted by your call to fulfill the Great Commission) or ... its time to reconsider what 'end of the age' really means in Matthew.
You could probably guess what I would recommend.
This is why I have said that when you interpret Matt 24 completely through the lens of "this generation" ... you will branch out in your consequence tree until it is as wide as possible ... then those consequences need additional foundation for support until the entire eschatological structure stands on a pin ... like a diamond balanced on its point. That point is the date of Revelation as I have said. It all comes down to that ...
If the book of Revelation was written after 70 AD ... your position vaporizes into nothing. That intellectual fulcrum of commitment is too much for anyone to uphold. It requires constant maintenance and the emotional and intellectual energy expended in defending it is better used elsewhere.