Can hags still cast when members of their coven die?

My last D&D session included a fight against a coven of sea hags. Hags have some interesting and a bit ambiguous rules about how the coven works. One of the rules was this:

Shared Spellcasting (Coven Only)

While all three members of a hag coven are within 30 feet of one another, they can each cast the following spells from the wizard’s spell list but must share the spell slots among themselves[…]

The question is do the hags have to be alive for this to still work. The party focused attacks on a single hag to reduce the threat, but would killing one member of a coven have stopped the spellcasting? Would killing two have stopped the last member from being considered a coven and being able to cast?