Does a jet engine keep running when it can no longer be controlled from the cockpit?
General rule here: the engine will remain at its last power setting should the FADECs lose comms with the flight deck controls (in your A380 case) or the thrust lever cables come unhooked (in the case of an older aircraft with mechanical cable-and-pulley controls).

However, the fire handle will kill the engine even if the main controls fail -- it operates the firewall fuel and hydraulic shutoff valves.  In QF32, this didn't happen because the cable for the #1 engine fire handle itself was damaged by shrapnel entering the wing.