Unless there has been a massive rethink, I doubt that the next Giulia will be RWD. It will be available with AWD I'm sure but to go for RWD only demands a new platform, new running gear and drive train and just seems too expensive for the volumes they will sell. It will also delay introduction which is already several years behind the death of the 159.
RWD does definitely harm the packaging of small/medium sized saloons. The Giulia is aiming for a wheelbase of around 2700mm, the same as Dodge Dart, Alfa 159, Alfa 166. The BMW 3 Series has gone to a 2810 wheelbase for the 2013 model - within an inch of the E39 5 Series.
Without Giulietta, the FIAT Group will need a much better FIAT entry than the ageing Bravo. Rumour has it that the Bravo replacement will be a crossover to cash in on the "Qashqai Effect", so somehow I think they still the Giulietta.
Having said that, Marchionne's strategy is very changeable, and structured by whim and rumour as much as shrewd business analysis. Whatever happens, he needs to get on with it - fiddling about didn't help Nero and its not helping Alfa Romeo either.