Printing counterfeit money in your basement and keeping it in your house and not spending it is still illegal.
Once the cat is out of the bag, and the mold is just sitting there, it's only a matter of time. Thieves cast others work, even for just themselves (oh, and just a few friends who promised to not say anything).
Thieves steal. Artists make it themselves. At least ask for and get permission from the original artist.
If 50 people bought this Han head and cast if in silicone just for themselves, there are now 100 copies. No one is going to be buried with these things, eventually they will leave your house, be out in the open, something will happen to them.
The more copies, the less the quality of each and the less valuable the original sculpt is.
Way to slap the original artist in the face. There is a line, you're either on one side of it, or the other side.