I have built a village in the jungle where I've managed to raise enough villagers for the game to begin spawning cats and baby villagers. I've also name tagged many of the villagers and completely light up the entire area so no hostile mobs can spawn. (I can confirm this as no hostile mobs have spawned over the course of completing the village.)
   One night after going to bed, I wake up to find all of the villagers (9 in total) having spontaneously despawned. No other mobs went missing, however. I searched everywhere in case they had just gotten stuck somewhere, but neither they or the cats have continued to spawn in the village. There was no sign of zombies or illagers nearby, and there is no way for the villagers to die of fall damage, drowning, or any other environmental conditions.