Checking until a window doesn't exist

I would avoid using the Exists method on the window object itself in this case.  The issue is you'll take a performance hit of several seconds when the window no longer exists.  That's because "Exists" waits for the full amount of time specified in your Auto-wait timeout set in the project properties. You could reset the Auto-wait time per Hassan_Ballan's suggestion.

However, I would suggest using WaitWindow with a loop something like below.  As you can see, I included a counter/timer so that it doesn't get stuck in the loop if the window never closes.

Set myWindow = xxx.WaitWindow(wndClass, wndCaption, 1, 500)
  x = 0
  While myWindow.Exists and x < 10
    Delay 500
    Set myWindow = xxx.WaitWindow(wndClass, wndCaption, 1, 500)
    x = x +1
  Wend
  
  If Not myWindow.Exists Then
    Log.CheckPoint "Yippie!  The window closed"
    Else
    Log.Message "Sad face.  After waiting five seconds the window is still open"
  End If