If I book a return journey with Ryanair and miss the first flight, can I still take the return flight?
Does Ryanair have the sequential use of flight coupons rule?
Meaning if you miss any flight-segment on your itinerary all subsequent segments are canceled.
Does this rule apply if tickets are bought in one booking?
I've removed (subject to review) the "And what about other low-cost airlines?" part of the question. There are so many low-cost airlines in the world that asking about all their policies is far too broad.
Well, apparently, the reviewers didn't agree and "Please tell me the policies of hundreds of airlines" isn't too broad. \*boggle\*
Ryanair only sells one-ways or returns so the only case is missing your first flight and still wanting to take the return. That is possible without any actions necessary on your part as stated here on their website FAQ:
You don't need to notify us if you are unable to travel and if you can’t use your outbound flight you can still use your return flight.
So yes, if you miss the first flight you can still take the return flight and no, there is no sequential use of flight coupons rule.
The question is "can I still take the return flight" and you answer "no" but mean yes?