Here are the most important reasons to buy travel insurance before you leave for vacation:

In certain parts of the world, you are obliged to pay in cash at the medical facility at the time of treatment. These costs will be covered up by travel insurance, up to the limits of your policy of course.

If you suffer an injury or become ill in a remote location, or a place that does not provide proper treatment facilities, there may be a need to airlift you to the US or another country for treatment. Costs of emergency medical evacuations can amount to tens of thousands of dollars, and your insurance will cover this, of course within the limits set up in your policy.

As far as trip cancellation or interruption caused by death, illness or injury is concerned, travel insurance companies will generally provide coverage for yourself, your traveling companions and your immediate family members. Contact your travel insurance company to check what is their definition of immediate family members.