Collection Agency & Debt Management

I have several credit cards on which I've negotiated favorable agreements. I have one agreement with a collection agency who previously threatened to place a lien on my property an file jugement against me. I have paid all my agreements on time. But, one agreement is expiring and the original creditor will not give me a new agreement. I cannot afford the minimum now and they recommended I call a debt management company (non-profit) listed on my statement. The debt management company wants to negotiate with the collection agency to reduce my payment. I'm scared the collection agency will refuse and get spooked that I'm in deeper trouble. I worry they will then re-double their efforts and demand payment in full. Shoul I just continue with my current arrangement, or should I let the debt management company try to negotiate? What's the worst that can happen?