Many policies do not apply pre existing conditions to the death of an immediate relative not traveling with you, although they will apply them to those traveling. Therefore the expected death of a non traveling relative due to pre existing conditions is covered under many commonly available policies. Like I said check the specific policy because the details are important. Use Insuremytrip.com or squaremouth.com, their customer service will point you to the right policies. This is a common reason that people buy trip cancellation or interruption policies. Many, many people linger on for far longer than expected per the OPs parent.