The Lawyer will draft the invoice reminder, and a scary advisory that it's a bad idea to build a business upon stolen intellectual property and know-how. They will follow up directly with the CFO of the organization, professional to professional. It might cause the CFO to have a meeting to discuss the risks of not paying. The lawyer may decide to play a short or a long game. They may decide that it's simply not worth it to pursue further. In any case, once it's delegated, it's their professional opinion, and you accept it.
In this way, you've done what you can, and you've moved on with your life. If you get a check in the mail a few months (or years) later, great. If the concern about a check arriving in the future causes you anxiety, this one is also easy to solve, tell your attorney that the beneficiary of any money extracted is the local food bank. Then it's closed. You move on.