Forgot some lore elements from ARR and Heavensward and what's the shape of the world?

[Wyssahtyn]

Estinien just buggered off to travel more or less.

You would have first seen Shinryu and Omega during the closing events of 3.55, which concluded with the two incapacitating each other for a time. Papalymo used Tupsimati to do the sealing spell Lousioix did during the Battle of Carteneau to seal away Shinryu for a time.

Nero tol Scaeva disappeared at the end of the Crystal Tower arc, yes, presumably to pursue his agenda. He showed up in Heavensward at the Carteneau Flats during, uh, 3.4 or 5-ish, to hint at Omega.

The world is presumably spherical. There are technically timezones, but as the devs felt it'd be too difficult to implement such (I believe they stated such in an interview) so everything still runs off the Eorzean Time clock in game.