Can anything be done if the debtor files bankruptcy but the creditor was not notified?

Anti-bankruptcy provisions, as stated above, are generally unenforceable with some very limited exceptions. However, if a party that doesn't have notice of a bankruptcy than their debt is not discharged. Of course, there is actual notice and proper notice. The fact that you know about the bankruptcy can constitute notice even if you didn't receive official notice from the Court. You need to find a creditor's bankruptcy attorney to protect your rights.

That wasn't a very well crafted agreement. Contact an attorney that handles legal malpractice cases to see if you have a case against the person that drafted this agreement. You should have retained a security interest in the assets of the business you sold under this contract.

You need to speak to an attorney and go over all of the facts. Unfortunately, your debt is likely discharged even without notice. You can move to have the case reopened but unless you have an exception to the discharge, there is not much you can do. In your contract, you should have hopefully retained the right to retake the business if a bankruptcy is filed. Your contract, as your described it, sought to declare all amounts due if they file bankruptcy...the problem is Bankruptcy then potentially wipes it out.

If the loan was secured by the business, you could take the business back at the appropriate time. If the business has no value, you are essentially an unsecured creditor. If there are NO assets in the bankruptcy estate, you have little chance of recovering even if you were not named as a creditor. The provision that the balance becomes immediately due is meaningless in a no asset bankruptcy case and may even be an unenforceable provision. Also, even if it became immediately due when the BK petition was filed it also became immediately uncollectable and most likely his obligation to pay will be discharged unless you can, through an adversary proceeding in bankruptcy, prove he entered into the contract fraudulently.

There is not enough information to give you a good response.

Lots of promissory notes say that. It doesn't give you any rights greater than the right to file a Proof of Claim in the bankruptcy for the total balance due. Which is a good idea. If you have a reasonable suspicion that some fraud or concealment is involved, you should consult an experienced bankruptcy lawyer and lay it out before him or her. First make sure the lawyer has no connection with the lawyer representing your debtor. While the debtor has a duty to list all creditors, anyone could leave one out inadvertently. In any case, you do have actual notice of the bankruptcy case, so if it is still open, you can file a claim. There a number of complexities in the law of bankruptcy, so consulting an experienced lawyer in your area would be a good idea.