Yeow, dark! But it definitely could have happened that way. In fact, as recklessly as JKR threw around all the Morsmordres and such, I always wondered how it didn't settle into the landscape and the wizards like a blight. Something has to explain why their population is so low.
*cackles* Lucius behind, but Snape at his side as his partner. Oooh baby, Yesss!