Easy
This one is an easy one. To do this you would make a custom unit (probabbly bassed off of the actuall villager) You can name him villager or dont decay due or whatever you want. Now, theres an option on the editor that allows you to choose the decay type of the unit.
All you have to do is change it to does not decay, wich is an option and BAM you have a permanent dead dude, assuming he's dead...