Without knowing more about your husband's health (chronic health conditions, smoker, etc), it is hard to say why he is still coughing, though the Riba does list cough
as a side effect.
Keep in mind that Ribavirin
has a long half-live, and it takes up to 6 months to completely eliminate all the drug from the body. Even so, a worsening cough sounds like a reason to call the doc. I have heard of others here who have developed bronchitis after finishing tx.
Best wishes, keep us posted.