I see no reason it wouldn't be just as 'smashed into nothingness by Calamities' as everything else the Ancients made. Which means, yeah, theoretically it could still be standing on the other reflections, except for probably the First as you've mentioned.

Honestly, knowing that Pandaemonium is basically a high-security prison, I'd assume that wherever it (and by extension Elpis) was built, it was a pretty significant distance away from Amaurot. THat could still plausibly put it somewhere on Eorzea, but I think it's more likely it's just at the bottom of an ocean somewhere.

Incidentally: I hope Azys Lla got those pieces back. It doesn't deserve that kinda treatment!