Let The World Burn.

Sure the Sovereigns managed to break off some parts of the ghouls once in a while. But those parts simply warp back to the section where they were detached from. The only consequence is that the ghouls get weaker. But they won't stop their hunt and they will continue to grow stronger the more Vampires they kill.

Ragnarok observed to himself. "I shouldn't have been worried for the ghouls. The Vampires have prospered in the Underdark. It is working against them now."

This tactic of using Familiars to slow down Ghouls is just a preventive tactic. It might have worked when Vampires were few in number when the ghouls were just created. But now the Underdark is full of Vampires. There is too much stimulation for the ghouls.