Jesus indeed returned in his power and might "in this generation" in 70 AD, just as he prophesied he would, and he destroyed Jerusalem, using the Roman armies to accomplish his will.
I disagree. It most definitely happened in the generation that Jesus was speaking to.
It is impossible for Jesus to lie and so it occurred in that very same generation.
33 AD to 70 AD was less than 40 years, which was a generation, according to Jesus.
It was definitely fulfilled in "this generation."
The metaphoric first covenant "heaven and earth" of the Jews, which was "their city, temple religious system, and city," were destroyed, and so all of these passed away in "this generation" in 70 AD, which was within 40 years of Jesus' prophecy. Mark 13:30-31
The heaven and earth of the Jews passed away in 70 AD. Now, we have only the "New Covenant," which is the "new heaven and the new earth," of the Christians. Revelation 21:1
The "sea was no more" because the "sea" was a metaphor for the giant bronze water basin used by the Levite priests to purify themselves before they served in their temple. 1 Kings 7:23-25
In Jesus' New Covenant, there is no need for this "sea," the giant bronze wash basin used for priestly purification before the priest serves at the altar of the Christians in their church. Hebrews 13:10
I choose #4. Jesus returned in his power "in this generation," just as he prophesied. He, King of Kings, from his throne in heaven, used his own power and majesty to destroy the unbelieving Jews, their temple, and their city. The Roman armies did his will for him. Matthew 21:43
We do not know, and we cannot know, what the world will be like when Jesus returns at the end of time. We must remain faithful to his commandments at all times, so that we will be ready to meet him at any moment.
All of Mathew 24 and all of Luke 21 were fulfilled by the end of 70 AD. Jesus did find faith on the earth when he visited earth with his power and might in 67 AD. His followers did as he commanded and and so they "fled to the mountains" when they saw the Roman armies building encampments around Jerusalem. Not a single Christian perished when Jesus visited his wrath upon Jerusalem.
Uh, oh! I just realized that this discussion is way off topic so this is not the place to continue it.