I might have missed something, but how is Agatha under the Westview enchantment if Westview was returned to normal? Couldn't Wanda have used that transformation power to keep her children and Vision alive? Objects like the jump rope seem to maintain their altered properties outside of the Hex so I am a bit confused why her family dissolves.

Was she also unable to free the residents of Westview without keeping the Hex or just part of it functioning for her family to live within--I know Agatha mentioned that spells cannot be altered, though it seems like Wanda had already changed the Hex's properties a few times. Maybe its better to dissolve away than stay a prisoner within the illusion?