.. and that is why I draw a distinction between being denied boarding and being deboarded involuntarily.
FWIW, as I recall, when the airline doesn't get you on the flight you booked and can't get you back out on their own flights within some time period (2 hours? 4?), they are obligated to get you on a competitor's flight if seats are available. IIRC, there's an exception to that rule for weather but not for mechanical issues or crew changes. Maybe one of the aviation professionals here could either confirm or set me right on this?