Originally Posted by
mitotic
They both have been damaged, to be sure, but I don't think we've ever been told that they have sunken into the sea. The north side of Kezan was evacuated recently and is likely covered with some lava or molten rock, but I'd imagine the island, some wildlife, and some non-Bligewater goblins may still be there.
We learned very little about the fate of Zandalar. In the daily quest Mimic Octopus, Nat Pagle says, "A buddy of mine caught one of these off the coast of Zandalar a few years back. He barely made it back alive, actually. Pesky trolls, but great fishing!" A few years back probably refers to before the cataclysm.
On the Isle of Reckoning, Prophet Khar'zul says, "We NEED dis land! Da cataclysm destroyed our home!" So Zandalar is destroyed in some way, like Darkshore and the Barrens were for instance, but not necessarily sunk.
In the quest Decisive Action, Taoshi mentions that the Zandalari bolster Lei Shen's army with war beasts and troops from Zandalar, suggesting that there may still be a living presence on Zandalar.