Sometimes, online travel agencies (such as Opodo) sell return tickets where the outbound and return flights are with different low-cost airlines (e.g., FlyBE and Eurowings). After booking what is presented to the customer of the online travel agency like a single ticket, you receive two record locators, one of each low-cost airlines involved.
Now let us assume that the outbound flight is canceled due to bad weather. If the later return flight is not canceled due to bad weather, what are my refund rights? Can I contact the online travel agency for a refund of the complete journey, or do I have to live with only getting a refund for the outbound flight from the airline serving the outbound flight?
I am particularly interested in flights within the European Union, where the cancellation of the outbound flight happened after the check-in. Not asking for a friend.