What purpose did the isle Azys La serve? Main Storyline Spoiler.

[Avidria]

Some parts of the Lore and MSQ are confusing or not clear to me. The Azys La structure seem monumental and phenomenal. How can a civilization so advanced disappear without a trace. They could remain on Azys La and survive. If Azys La is intact it means the people on it could survive too just like the mobs living there. That place is just weird as it is. It looks so alien ish. That warring triad is a mystery. Are they the source of power that fuels the whole place? If they break free / die or whatever won't make the whole place fall down destroying it? Or it just a huge magical experimental flying lab / Alcatraz of some sort?

Hubris. From what I've gathered, the Allagans destroyed themselves.

The fall of the Empire is (somewhat) explained in the Crystal Tower storyline.