In my estimate, you could leave a tribe of fewer than 10 villagers, on slow, overnight. On slow, 1000 food should last that long, plus you know they can survive with zero food for quite a long time. I leave my game on overnight all the time, and though sometimes I come back to find them getting a bit desperate, usually they're fine.

If there is any food (even a tree regenerating a little bit), any villager with some farming skill will go get it.

You can backup your game and then you will not be risking anything, since if they die you can restore the backup. Even if you don't have a backup, you can save them even if you open the game and find every last one of them has died.