The airlines will have to bear to assist and return passengers to their hometowns, where they hired the cheap flights package. If the tickets were purchased separately at different websites, you can only recover the amount of the canceled flight.
The user can request a refund of the full amount of the contracted flight or flights, so if you have not done any as if you have flown one or more destinations for travel connections as the trip no longer makes sense.
If you have been informed of the cancellation after reaching a destination of the connections, the airline responsible for the flight you were going to perform at the airport where you are at that moment must provide assistance, food, drink and accommodation – and take care of returning you to the city from which the first flight were taken.
If the passenger is in this situation at an airport outside the European Union, rights are the same whether the airline that would fly is established in the EU. Otherwise, everything depends on international agreements or regulations affecting the airline or the country where the problem occurs. We recommend contacting directly with the airline if this is the case.
This is the more complicated situation for passengers, as they will only be able to recover the amount of the canceled tickets and not from the whole package.
As example of the above you bought a ticket from your country to London, and another ticket separately from London to Tokyo.