I agree that the agent should have simply said "sorry - too late" and ended the discussion there and not tried to invent reasons

It isn't up to the gate agent to choose whether to risk a delay to the flight and to not close the flight

It would be up to the operations area to make a determination on whether to hold the flight for the connecting passengers - if it had, the agent would ( I assume ) have left the flight open

If the agent has not been asked to delay the flight closure, then the agent was doing their job correctly in getting the flight departed

Was it US airways that chose to pause the inbound aeroplane or was it the airport? The airport operations may have needed to pause operations, but it is then up to the airline to decide what it will do in this case

It is not great to be delayed overnight, but my response was that I could see no grounds to complain as put forward by another poster ( which I inferred was complaining about the agent ) - other than the silly excuse for which I don't see what would come of it other than a stock reply saying how they understand how you feel but that the flight was closed and basically it sucked to be you that day