The thing to look for in the NDA is an assignment clause. If there is one, and the assignor (them) doesn't need to give you notice in advance, then they can assign their rights to the NDA.
Your best bet is to hire a lawyer to look up the company to see what business form it actually had, to review your NDA, and to discuss your possible defenses to it.
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You are still bound by the NDA, but the question is to who. Who, is the successor to the LLC, if there is an assignability clause, which is routinely present ["this agreement shall be binding on the heirs, successors and assigns of the parties" - or something similar]. If yes, then the sole proprietor can simply assign it from the LLC or partnership to his sole proprietorship [i.e. to himself] in order to enforce it. Whether you were an employee or independent contractor will not change the outcome if there is an NDA you signed. More likely determinative in Illinois is whether the employee had the right to assign you additional work, what benefits were paid, how taxes were reported, etc. Before you presume invalidity of the NDA and proceed to violate it, better see a lawyer as otherwise that could really backfire on you.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.
Your ask if an NDA is still effective following a series of company changes. Based on what you have written I would say "Most Likely Not." I say that because you have not indicated if the NDA included a "reasonable scope," a "reasonable geographic area," or was for a "reasonable period of time." All of these somewhat nebulous standards must be met in order for a Non-Disclosure or Non-Compete agreement to be effective in Illinois.
I would recommend that you progress beyond this forum and find an Attorney familiar with such documents that can take a look at the actual language in conjunction with a detailed breakdown of the history of this matter. Only that Attorney will be able to give you a credible answer; but he or she should concentrate in business matters.
I hope this information has been helpful. Feel free to contact our office to discuss this matter in greater detail.