Midgardsormr and the Airship in Mor Dhona!

[Fleurette]

It was one of those Evidence A + Quote B = Rigid Interpretation C kind of things. (The same kind of thing that led me to believe the sylphs were referring to physical changes in the beast tribes that summoned primals, which of course led to hiccups with some interpretations because the Ixal have been physically changing as a result of Garuda's influence for far longer than they've actually been summoning her.)

Evidence A
Both NPCs and the local introduction story arc made it seem like the Empire, being just outside their doorstep at Ala Mhigo, were going to move on Gridania next (and they were planning on fighting back).

Quote B
Whenever 2.0's world revamp came up, one of the first things mentioned was the shroud, which everyone hated navigating due the constraints rigid options. It took forever, and gave some of us FFO veterans flashbacks... I could practically smell Yhoator outside Gridania.

Rigid Interpretation C
The Empire is coming, they're going to hit Gridania really hard, we're going to have a better forest in the end.

Luckily we get a whole new world, instead!

I doubt Bahamut missed on purpose. The game didn't go out of its way to show this, but Mor Dhona and Cartenau aren't that close. Silvertear Lake itself, where Midgardsormr's corpse lays, is far enough away to be outside of the big attack, provided it was missed by debris (which it seems to have been).

Cartenau Flats is pretty far southwest of the lake inside Mor Dhona. In fact, Cartenau is as far away from Silvertear Lake as Ul'dah is from Cartenau.

Aha! That makes a little more sense, then. Thanks, Mr. Moose!

Also, yeah, now that I'm looking at the map I realize how far Carteneau was from Mor Dhona/Silvertear Lake. For some reason I'd always assumed Carteneau was a part of Mor Dhona itself, probably because of how it was implied in-game and because i thought they wanted to have kind of a "full-circle"-esque effect where it all started at Silvertear Skies, and it'd end in the same area. But seeing how far away it is, yeah, Bahamut probably didn't even want to bother with the Silvertear area. (for lack of better phrasing. :P)