IIRC it depends on if it was ordered with FSD or bought it as an upgrade. My understanding is if it wasn't originally ordered with it, the new owner has to upgrade again to get it.

(Since its on the monroney label they have to keep it for cars that are ordered with it originally)

It follows the car if you sell directly to another person or through a third party dealership. If Tesla gets the car back, they'll wipe the upgrade and charge for it again.