Quote Originally Posted by The Man
well, they could go and laugh at the poor aeon people who were trapped in their summoned state in a summoned city

edit: actually, that raises a good question to me. If they had intervened in the summoning by destroying what was being summoned, would Yu Yevon likely have reacted in some manner? Would that have destroyed Sin, even? it might be easier to level a city than to defeat a giant space whale.
Well, as you see in the opening FMVs of the game, the city gets leveled by Sin itself, so that doesn't in any way impede Sin's existance. More likely than not, however, Yu Yevon just repaired the damage and removed any memory of what took place from the minds of the survivors.

Sin isn't an Aeon anyway, actually. Sin is just a whole lot of Pyreflies held together by Gravity Spells.