A script to launch the Things Quick Entry Panel when the app is closed.

OopsieThings.applescript

set GTDAppName to "Things"
global GTDAppName
set GTDAppToUse to FindRunningGTDApp()
if (GTDAppToUse is null) then
	set GTDAppToUse to "Things"
end if

on AppIsRunning(GTDAppName)
	tell application "System Events"
		return (count of (application processes whose name is GTDAppName)) is not 0
	end tell
end AppIsRunning

on FindRunningGTDApp()
	if AppIsRunning(GTDAppName) then
		null
	else
		tell application "Things"
			activate
			show quick entry panel
		end tell
	end if
	return null
end FindRunningGTDApp