It depends. I am not sure from your question whether you contracted with a corporation or an individual? If it was a corporation, is it still doing business? If so, you can enforce your rights against the corporation.
If it were an individual, you can enforce your rights against the estate if you have already provided services, or sold goods, under the agreement.
Are you posing the question to determine whether your obligation is extinguished or the obligation of the party with whom you entered the agreement.
Without knowing more, I can not be anymore specific. Hope this was helpful.
If, as you pointed out, the firm was incorporated, the answer will turn upon whom the agreement was with - whether it was the individual in his sole (individual) capacity or in some capacity (or agent) of the corporation. It could be that the agreement did die, but it is just as likely that it did not. Whether you are still, in reality, bound by the agreement will also turn on what the agreement concerned, the value of the agreement, whether the corporation will continue in the "proprietor's" death, and so forth.
Your best bet is to pay an attorney for an hour of time to review the document and discuss this issue with you.