I was looking through the Secrets of Sarlona and Player's Guide to Eberron, and read the Eberron fluff for maenads.
Two thousand years ago, one of the islands of the Lhazaar Principalities sank beneath the sea in a magical cataclysm of unknown origin. Most of it's people drowned as the ocean boiled, except those who were at sea when the cataclysm occurred. When these folk returned from there raiding and fishing, they found only open water where there home had been. The survivors banded together and sought a new home, which they found on the Tashyvar Islands at the northwest end of Sarlona. Whether from the lingering effects of the magic that destroyed their home or due to some property of this new land, their physical nature was altered, transforming them into maenads. Their grief at the destruction of their homeland is the most likely source of their racial anger, though some suspect that anger to have an earlier root that might be linked to the cataclysm.
This is the same fluff that's in Secrets of Sarlona, except it also claims it was a great human civilization that once existed among the islands of the Lhazaar Principalities.
So, is it just me or does this sound a lot like the destruction of Thanaclan? Can I use this in Savage Tide?
Looks good to me!
The only difference is that Thanaclan might be sunk away, but there is still an island, namely the Isle of Dread. If I read your description well, the maenads have no land at all. So you would have to adapt that.