Which procedures or devices do ensure the aircraft stop flying after the pilot has ejected?
As you pointed out, the only reason for abandoning an aircraft is because the pilot can no longer control it or successfully land it.  With or without flight crew onboard, it's going down in one form or another.  As such it's pointless to design any additional system to disable or destroy the aircraft as it accomplishes nothing.

Pilots however have been known to direct a stricken or otherwise doomed aircraft away from populated areas, as this Thunderbirds pilot did at a 2003 air show at Mountain Home AFB, in Idaho.


                
            

So too was this crash of a MiG-29 at the Paris Airshow in 1989.  Mikoyan test pilot Victor Kobachev ingested a bird in his starboard engine and the jet departed controlled flight;  Kobachev fought to direct it away from the crowd line before he punched out.