I have spoken to a lawyer, and I've been told that legally I have absolutely nothing, and the original writer of the code has legal rights to require the discontinuation of the code at any time.
Could you please have your lawyer contact me on
leo@bustabit.com and reference the details of the sold license? I will happily, free of any additional charges, work with your lawyer to provide all the guarantees you or your broker require (i.e. signing the necessary contracts, permissions, licenses, etc.).