Decompression zombie aircraft-a simple solution

There should be a interlink which brings engine power to flight idle
any time cabin pressure is lost above FL180. The aircraft wil descend
under autopilot. There is statistically very little terrain above
18,000 feet and what there is is unpopulated.

Of course there should be an override, but it should take positive
crew action and should need to be repeated at intervals.(The emergency
buoy on a sub, is a good example. If not manually held down with a
timer button each hour it releases and sends the rescue signal.) How
long is a passenger aircraft without cabin pressure gooing to be
operated abov FL 180 anyway?