Seems like they're preparing a new part of Time Temple.

But there's nothing that suggests that a fall of such great height would cause Maple characters to die, either. Are there any precedents? I doubt there's ever been a story-based scene involving someone being flung off a high place prior to this. And even then the flinging's implied.

You've got me there. As far as I know, there are none.
I'm simply basing my logic on the generally accepted idea that, in most fiction, there's a limit to how far people can fall without taking unsustainable injury.
Maplestory could be an exception, of course.

My main issue is that it'd seemingly be a retcon to have the battle against the Black Mage take place inside the Temple of Time.
Then again, I've already become confused by the fact that the Heroes apparently didn't all fight the Black Mage simultaneously.