Do they wait until all aircraft have landed before winding up an airline?
The article speculates based on a single precedent:


  It's likely (looking at the precedent of Monarch's collapse) that any announcement about that will be made late at night, once all planes are on the ground.


But evidently that's not entirely the case. Thomas Cook ceased trading at 0109 UTC of the 23rd, with some of its planes still in the sky:


(Flightradar24) Showing only TCX callsigns.

As you can see, some of them are long-haul returning from USA. I also could not correlate last departure time with the announcement. The latest I found was at 1131 UTC (MT2643 from Orlando to Manchester).