Upvote:0
In practical terms, you cannot be stranded by the airline before departure from the origin airport on any flight sequence. That you have booked a round trip ticket really doesn't matter since a round trip is just two origin/destination pairs booked together.
The airline is only obligated by contract to provide you transport for which you have paid. So, what will happen is:
No. 3 - They reaccommodate you on another flight, possibly operated by another airline.
No. 4 - They refund any unused fare without penalty.
Local regulation may strongly favor #3 but it may simply not be possible in within a timeframe that suites the traveler. For example, recent hurricanes close many airports for several days so you may have to wait for a week or more for reaccommodation.
For the nitpickers, it doesn't matter that you're away from home. And for clarity, you can be stranded by the airline at some point in between the origin and destination, including a connecting city.
Upvote:1
If cancelation isn't due to force majeure, then:
(a) Provide you with alternate transportation back home at no extra cost.
They can't leave you stranded, even if flying you home coats the twice what you have paid.
(b) Same thing - they're required to bring you home.
They don't have to use the same stops, or any stops.
(c) They may offer alternative transportation or your money back.
They're not required to bring you home. As far as the airline is concerned, you are home. If they cancel your trip, they owe you no more than what you have paid.