Despawning of villagers and all mobs around them?

So, I’ve had a large villager farm for a few months in my world now, and I’ve started working on achievements. The villagers are all were all high leveled, and I had about 32 villagers in it. One day I had come back from a night at the swamp I was at looking for slimes to complete the slime block achievement, and went to trade with my villagers (attempting to get the 1000 emeralds achievement) and they, and the iron golems, and the sheep and chickens farms that were with them had all disappeared. At first I thought a zombie must have gotten in and killed everyone, but my setup was impossible for zombies to spawn in, and all the iron golems and farm animals had gone too. This was not the first time I had traveled away from home, so this was very upsetting. All the villagers and mobs around it had just disappeared, and there’s no villages for miles that I can replenish them with. I wanted to ask if this happened naturally? Also they couldn’t have been killed by zombies because I was way out of render distance. I am very upset that this happened, and the worst part; I didn’t even get my slimes that night, just zombies ( that I was going to sell the flesh of to the villagers ). Anyways, I hope you can get back to me on this because I’m gonna cry myself to sleep tonight lol. ( I was at 543 emeralds trades ) now put that into the level and time I’ve spent on each villager. Anyways have a good day or night. Bet you didn’t read this through but thanks anyways lol.