With regard to the no fuelling aspect, the re-fuellers at my base normally just turn up connect the fuel hose to the aircraft and start pumping (they already know how much via a message passed to them earlier), and would not normally know (or care) if the flight deck was manned. The cabin crew would noramlly be busy supervising the pasengers etc, are they supposed to keep one eye out of the window to check to see whether the re-fueller has turned up and then run outside to stop fuelling until flight deck crew arrive ?
Medical emergency ? ..... Pasenger has heart attack after climbing up the steps, the quickest way to summon help is often via the radio (ATC/Handling agent), difficult with no flight deck crew ......