but worse still could be fuel consumption at the lower altitude if forced out of RVSM.
Even worse is the subsequent failure!
A flight restricted to FL250 due pack failure increased the flight plan fuel by 250kg from BCN to blighty...FL280 isn't going to be as much!
The reason for the no autopilot is that the independent sources of data cannot be monitored. i.e. Capt SG fail, if 'A' autopilot is engaged you do not know what modes it is operating in as you cannot see the FMA's. For 'B' autopilot, a slow roll of the IRS would mean the aircraft would slowly roll too, along with ALL EFIS displayed AH's (watch the standby!). So if you are flying, you will detect the failure mode earlier...
Lastly, when you get the failure, after the QRH is done you may want to 'check' the other SG by going EFIS XFR Switch back to Norm. On 95% of occasions things will be back to normal...Happy days!