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 all three of 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 their spellcasting? Would killing two have stopped the last member from being considered a coven and being able to cast spells?