When I first came to see as truth the fact that the Lord had come in 70 AD and all prophecy had been fulfilled my first objection was, "This means we are living in the new heaven and the new earth!" My response to that was "Yea right! If this is the New heaven and earth we got ripped off." Why did I feel that way? It was because I was looking for a physical fulfillment of 2 Peter 3 and Revelation 21-22. I thought that those passages were speaking of physical truths, I now know differently, I didn't understand apocalyptic language. The thing that changed my mind was seeing how the OT Scripture used the concept of heaven and earth. Lets look at how the Bible uses the concept of heaven and earth, I think you'll see that it is not always used physically.
Jesus does not have in mind here some specific statement of prophecy. He is not talking about a judgement of Israel, he is not speaking about a specific aspect of his atonement. The Jewish idiom "the law and the prophets" means the totality of the OT revelation. Jesus said he did not come to destroy it but fulfill it. Jesus is saying here in Matthew 5 that the old law has to be fulfilled, every jot, every tittle has to be fulfilled before it can pass away. If 2 Peter 3 is based upon the OT prophets, and it is, and if 2 Peter 3 has not been fulfilled then we are still under the OC law. That is quite simple. Do you believe that we are in the NC? If we are then the OC must have passed away. And if the OC has passed then 2 Peter 3 has been fulfilled.
The passing away of heaven and earth is another way to speak of the end of the Old Covenant.