I purchased a tkt with the travel cancellation insurance to go see my grandmother who was ill in Europe. I had to anticipate the departure date as her condition was getting worse but priceline's difference in price for the new date was like purchasing a new ticket.
So I bought a new ticket through another agent thinking I would get re-embursed for the first since I had travel insurance. My grandmother passed, and even though "death" was a valid enough reason for cancellation and they had the death certificate and everything, Priceline refused to re-emburse because my grandmother was not an American citizen They told me I would have credit to use on a future flight by October 24th, but when the time came to rebook (October 13th) they told me my credit had expired in June.
So, you're looking for a reliable agent, use somebody else unless you want to throw $850 away.