TIF (April 2019) policies, including the Aggregators, HX Plus Cruise, HX Go Plus, DO NOT cover ‘End Supplier Failure’ but they do cover ‘Scheduled Airline Failure’.
This basically means, if their flight has been booked independently from their holiday, they can claim but if their flight was booked under a packaged holiday, they would have to seek reimbursement through their holiday company aka ABTA/ATOL protection.
To read information about how much Scheduled Airline Failure is included in our TIF April 2019 policies, please refer to pages 28-30 approx and for our Aggregator policies, please refer to page 13 approx, that mentions it as "if your scheduled airlines stops trading."