Guess you are blind to the irony of that statement, since what started this was that we do, in fact, have a prediction of consequence for moon-planet collision and what you said is patently false.
Think of a nova. We've never had one happen but there are some audacious conjectures as to what would happen. As well as the myriad of other events whose consequences are known well in advance of their occurring.
Also, ancient fucking
(an entirely necessary addendum) greeks were not capable of manipulating their observable universe. Something that would suggest that beings who are, might be more privy of the details regarding how that shit
(another vital addendum) works.
Currently your working theory about the ending shapes out to be "elves crash the moon onto pale rock in order to kill the dragon/naga, but annihilate the planet instead. Whoops"
Lowlands->swamp:
Idk what to tell ya.