They probably died of old age. Whenever the GC makes a party, any sick villager is healed. As to the food supply, since the GC will occasionally go to the food bin and magically create food, he should be ok. The only question is whether or not an event will pop up. Well, good luck on that. I have one game running where I have just one VV that is sick and there is no one to heal him. All the others died from starvation. I'm hoping for a barrel of babies because even as young as 2 years, a VV can heal another.
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"Hope is the feeling you have that the feeling you have isn't permanent."
-Jean Kerr