Sometimes their tour can be spoiled in the event of travelling cities during flight, if it is delayed or cancelled, baggage loss or if one gets medically ill, or any injury or sickness due to accident or even hospitalized for any other medical reasons.
Health care issues are always unpredictable and to be on the safer side, it is necessary that your parents purchase visitor medical insurance and get complete protection against healthcare emergencies. There are lot of companies that are offering health insurance plans either from their home country or after landing in the United States. Buying a good visitor insurance or visitor medical insurance from a reputed US based company is very important so that it gives maximum coverage plans that suits their need.
For more details, read how to buy and quote visitor medical insurance plans, or review and buy one of the popular plan choice among Indian relatives or parents visiting USA such as Atlas America Insurance or Patriot America Insurance.