Since Mixcrate is an LLC, why didn't they just wait it out? If the other company really sued and bankrupted the LLC - so be it. Shut it down. Why shut it down because of a "letter"?
I have zero knowledge about this stuff, quick googling returned a result[1] which says the owner might be held personally liable if "intentionally does something fraudulent, illegal, or reckless that causes harm to the company or to someone else"
[1] https://www.nolo.com/legal-encyclopedia/llc-basics-30163.htm...