Another easy way that UAL incident could have been solved. Was there a JS? If not, as a DH, I'd have no problem taking the jumpseat to get a paying pax on... assuming no jumpseater. Hell it's only a 40 minute flight?
True story example:
I was scheduled to operate a flight from SFO-EWR at 230pm. It cancelled for weather. CS put me positive space DH on the redeye (we only have one) from SFO-EWR that night. I wait and hang around until boarding is finished, and it's just me and another young woman standing there. I ask the gate agent what the situation is, and she says the flight is full, I have the last seat. I ask what would happen to the remaining woman passenger, and the gate agent tells me she would have to be re-booked on a flight tomorrow. The young lady is very sad, almost in tears. As it also turned out, she was supposed to be on my original flight at 230pm. So she's been screwed in a same way as I had in terms of delay and inconvenience.
So, I asked the gate agent if there were any cockpit jumpseaters. She said no. And with that, I said put me in the jumpseat, I'll ask the CA (who I already knew personally), and give this lady my seat in the back. This passenger was so happy to get on the flight and thanked me for making it work out. And yeah, jumpseating on a redeye 5 hr flight isn't much fun..... but there were no jumpseaters, and I have this job because of people like her who buy tickets and help get me the paycheck. Besides, she was screwed just like I was because of weather. Why make her suffer longer? I have zero regrets with that decision.