I don't think that the Black Rose Catastrophe was necessarily a World Ender worse than any of the other calamities. The Calamity of Water wiped out whole landmasses and set humanity basically back to the Stone Age. The 7th Umbral Calamity (Bahamut) was basically exceptionally tame by Calamity standards since most of the civilizations survived it. This is called an Umbral Cycle, where civilization has to rebuild, and much much knowledge is lost. Normally recovering takes hundreds or even thousands of years, at which point a new Astral Cycle begins. What Graha'Tia saw was a world amidst an Umbral Cycle, the state of incredible loss. Society would probably eventually recover (the Garlond Ironworks was apparently even still active in some capacity) but millions of lives would be lost and it may not recover in any shape recognizable to what it was.

To the Ascians it would be business as usual. They'd wait for civilization to rebuild enough, start up the process of unbalancing another shard, and then trigger the next calamity.