What you told me of the naga before has been plaguing my mind. Who are these allies they're summoning? Do they really think they can defeat the Tidehunter?
Escaping this cave brings a degree of relief, but our purpose here remains. I'm hoping you will be willing to seek answers from the Battlemaiden one last time.
There's only one place that I can think of where they would have taken the artifact - the temple atop the ruins. it's sure to be well-guarded. Proceed carefully.
Progress
The ruins are surely still swarming with naga. Pay close attention to their patrols and I'm sure you'll be able to slip through.
Completion
Minions of the Old God? Two very potent foes have joined forces then. Their hope to defeat the Tidehunter may not be so foolish after all.
<Name>, we can't let that happen. If Azshara defeats the Tidehunter and takes his power for herself, I'm not sure any number of us could ever hope to oppose her on the seas.
The first step is clear at least - we need to hunt down the fiend that destroyed our ships. The navy was confident enough to bring in a new fleet, perhaps they have a plan.
Swim to the very top of the ruins and enter the temple. Swimming by the crucible in the middle...
The crucible looks abandoned and powerless. Perhaps there is a place nearby where you can attune yourself to the Battlemaiden...
Said location is on the upper level of the temple[33.1, 77.8]
, on the ledge above the temple's entry. Back in the battlemaiden phase, Sira'kess stands in front of the battlemaiden, offering Devout Assembly, which has the full details. After Final Judgement, head back to the cave.