Just like any personal loan or debt, being owed by a sole proprietor who passes away -- you need to get in line with the other creditors to make an application to be paid out by his estate.
I am assuming you wrote it out to a person directly, or to a sole proprietor company name.
The recourse is to send a formal letter, requesting the money back from the deceased's estate, include a copy of the check, if you can. The executor would then pay off debts (like outstanding credit cards and you), and then pay out to the heirs. This process can take a few months and if there is insufficient funds, you may not get all of it back. Preferential creditors are paid first (government employee taxes, first line creditors, secured creditors) and then the secondary creditors would normally get paid out from the remaining estate.
You can also notify his bank where it was cashed that he died, you are owed money back and that the bank account, if joint, should be frozen. (Which is very crappy for the other people living with him, if it was also the main personal household account, I wouldn't do that for $550, myself, and this is why business accounts should be separate from household accounts). The business account may not have any money in it either, as often deposits from one job are used to cash flow / pay off the labour from a prior job.
A letter should be sufficient if they are working above board.