Pioneer Tours and Travel highly recommends travel insurance. Most policies include cancellation at any time. Here is a link to a site with many choices:
Pioneer offers a refund of the $500 deposit within 20 days of reservation deposit receipt; 75% refund (less $500 deposit) within 180 days of departure; 50% refund (less $500 deposit) within 90 days of departure; 25% refund (less $500 deposit) 60 days or less of departure; and 0% thereafter. Generally you can do better with travel insurance. According to the above site, one of the policies, named best for seniors by Forbes, is Tinleg, for about $393 per person for the tour (not including airfare, which you can purchase along with your flight).