I was on the frequency yesterday when Southwest 2919 declared an emergency due to failure of their ‘A’ hydraulic system (no fluid light). Everyone handled this in a very professional manner, although it was notable that at some point in the emergency the crewmembers exchanged pilot flying - pilot not flying roles: a different voice started talking. There were 155 souls on board.
It looks like they got going after about a 2 hour delay. I do not know if they repaired the aircraft or brought in a new one.