You need to remember that there is a difference between selling the copyright to something, and selling a license to that copyrighted material.
If you up and up sell the copyright, that means you are giving them all rights to do with as they please, and unless otherwise stated you will have no control of any kind after that point.
A license however, is an agreement that lists out what they can do with a copy of that which you hold the copyright to. So, what does your license say?
Originally Posted by Lrrpie-CT
I destroy drives for clients all the time. Sometimes, intentionally.