Over the years on B747 100, 200, 300, 400 & SP I have been involved in shutting down 5 engines, 4 RR & 1 GE. Even on the SP which as you no doubt recall was kinda fast in crz, the A/C gen went off line rapidly.
I find your friend's claims about A/C gens remaining on line with the engine shut down unsupportable from my own personal observation. Not theory, observation.
Mustavagander, I believe you, but my 744 pilot friend has restated that his generators stayed online (on two occasions). Not sure what engine he has on his aircraft though... Maybe he has P&W.
I'll keep digging.
Rgds.
NSEU