Please add some mods or directly in the game, someting that will make hearthling killed by zombies to revive as enemy zombie.
at this point, the clossest thing to what you are suggesting, is the debuff the hearthlings get when they are hit by a zombie i guess?
There was something like this in the halloween mod, where your hearthlings degenerated after getting biten by an enemy (zombie).
In the base game this would not really be an interesting feature, but as groms said the halloween mod has such an option.
As hearthlings can’t even die of their own age yet and random events do not exist, this would just be overkill for vanilla.