Title.
All we know about Y’shaarj is it was an Old God pulled out of Azeroth by the Titans long ago (creating the Well of Eternity, a wound) and killed. In doing so, the breath exhaled by the corpse is what created the Sha.
However, when you take a look at Xal’atath, it’s heavily hinted she isn’t merely a minion of the Old Gods. It’s very much hinted she could very well be a full Old God. But the Chronicles Books were very clear that only 4 Old Gods ever landed on Azeroth.
Following back the lore we know about Xal’atath the Dagger - no one knows where it came from. It simply appeared one day. If you read about Xal’atath in the Priest Class Hall, you learn no one knows where it came from. The only rumors are that it’s a Claw of Y’shaarj or the remains of a forgotten Old God (which Chronicles establishes can’t be possible).
So, I throw out a theory - What if Xal’atath IS Y’shaarj? What if, when it felt itself being ripped out of Azeroth, it clung on, and sent its consciousness into its claw, then detached it, created the dagger known as Xal’atath?
Then the body the Titans killed was an empty husk, which is exactly why the way Y’shaarj died was completely different than C’thun and Yogg-Saron, who did not expel anything when they died (which have been confirmed dead in multiple interviews now). Instead of an Old God dying, the Titans only killed an empty husk, which is why the Sha were expelled.
It would also explain how Y’shaarj’s heart was still active so long after its death, if Xal’atath is still alive, then its heart would still have a power source. It wouldn’t need its heart to be alive, but it would still be powering it.
Y’shaarj was known as the most powerful and wicked of the Old Gods, so wouldn’t it go to reason it’d have a stronger sense of self preservation than the other Old Gods?