IDK if this will make you feel better, but apparently that's a thing people have been doing - signing up for exchanges and then deleting their accounts without any notice to the mods (and it doesn't seem to trigger a default notification on AO3). I know of at least one other exchange where the mod(s) had to deal with this kind of deletion/pinch-hit scramble, so at least you are not alone?
no subject
Still, what a dick move.