Recently I learned the hard way that Not flying the first leg of the journey – Company cancels the second-leg ticket, since companies do not allow to fly only the second flight. This is also something IATA explains in Coupon sequence and use.
I was flying from a city in Spain to a city in Portugal with TAP Air Portugal on a return ticket.
When about to take the first leg of the ticket we were several people, including my wife, our little baby and me. We did the check-in online, with my baby attached to my place (she is few months old, so she does not have a seat on her own).
When in the airport we went to the baggage drop area and were asked for the passports; we showed the 'libro de familia' (family book) that works to fly in a domestic flight in Spain, but they told us that is not enough to fly within the European Union. Since the baby did not have a passport, she could not fly.
After some discussion, my wife opted to stay with the baby (she needs breastfeeding, something I cannot give :P) and solve the issue, while I took the flight (to minimize the loss of money). Also, I had to redo the checking, since the baby was not flying with me anymore and I was given a ticket on my own.
So the schema is: leg 1, me flying, while my wife and baby staying.
Next day, my wife solved the problem and her and the baby flied to the city in Portugal with the same company.
Some days later we went to the airport in Portugal to take the second leg of the return ticket. To our surprise, my wife's ticket had been cancelled because 'she had not taken the first leg of the flight'. We had to buy another ticket for her and finally made it home.
I was quite curious about my baby not having to pay again for the ticket, since she already missed the first leg of the journey. However, my main question is: what can I do in the future to preserve the second-leg ticket if I notice that I am not going to be able to fly the first leg?
I assume this can be easily (and costly) solved with days in advance by changing your ticket. However, my question is about this happening while you are already in the airport and the flight is about to leave, without you in it.