The gospels did exist for decades, there is much evidence for that. I don't know what prophecy you speak of or what warnings Jesus taught.If the gospels existed for decades then the destruction of Judea was a fulfilled prophecy and the consequence for failing to heed the teaching and warnings of Jesus to the ruling elite about false roman security and the illusion of prosperity at the expense of setting aside their professed dedication and allegiance to God and truth and abandoning the majority of the flock to the enemy for slaughter.