The claim that Jesus taught that is important to both Preterists and Bible Skeptics. But, I've never seen a preterist try to debate a Bible skeptic, to try and convince a non believer that Jesus clear Prophecy of every eye seeing Him was fulfilled in 70 AD.
The strongest argument is when Jesus said "There be some standing here, which shall not taste of death, till they see the
Son of man coming in his kingdom." in Matthew 16:28, Mark 9:1 and Luke 9:27.
The argument that this was fulfilled by the Transfiguration I could accept being written off as a silly cop out if The Transfiguration directly followed this in only one of the accounts. Often the different Gospels will at face value seem to contradict each other's chronologies, and I believe there are answers for all of those issues. But the point here is, all 3 times this was said the Transfiguration immediately follows. Even if I thought the Gospels were fiction, as a writer myself I'd see the clear connection there.
Now the Olivite discourse saying "This Generation shall not pass" has been discussed in depth by many. The context clearly says the generation seeing the signs he just described. Others have gone in detail of why the Greek grammar allows no room for the preterist view. I'm not sure exactly which previous online discussion of it I want to link to here yet. But what I'll say below puts the greater testimony of The New Testament in favor of the futurist view.
In Acts 1:6-7 Jesus deliberately discourages the Disciples from thinking he would return in the near future.
In 2 Peter 3, the Apostle Simon Peter speaks of the Last Days in a sense that clearly implies days different from the then present. He foretells the world rejecting a literal interpretation of Genesis when Christianity hadn't even become the mainstream religion of The World yet.
Paul in Second Thessalonians 2 assures his readers certain things must happen first, and gives no indication they should expect it to happen anytime soon, quite the contrary he's telling them not to worry about it.
I also like pointing out here that there are Prophecies in the New Testament that did come true. All three Synoptics but especially Luke foretell what happened in 70 AD. And I've argued that the Bar-Kochba revolt is in Mark. Skeptics of course insist on late dating those Gospels, but I firmly believe all 3 Synoptics predate 70 AD. But even among skeptical scholars only the most extreme try to place Mark later then 90 AD.
In the Kingdom Parables in Matthew 13, the implication of at least 1 parable, the Mustard Seed, is that Christianity will become the world's largest religion someday. And there is no way with even the youngest possible dates for the Gospels they were written at a time when that seemed remotely plausible.
And as I just alluded to, 2 Peter 3 foretells the theory of Uniformitarianism and Christians rejecting the idea of a literal Second Coming because they've rejected a literal understanding of The Creation and The Flood. Even if you are an Atheist who thinks those Peter is criticizing are correct, there is no denying that Peter could not have expected that in either the first or second century.
So The New Testament has proven itself to be Prophetic.