A company like PD couldn't exist without a company like Sony.
Consider this, Team Bondi released LA Noire, a game initially funded by Sony, published and funded later by Rockstar. The game sold well, was quite well recieved... due to poor studio management, the costs involed and the time it took, the company is bankrupt.
PD without Sony would suffer the same fate and Sony are stepping in NOW to let them continue to make the games but also to stop bleeding money, because blank cheques for PD can't continue.
There's studios like Naughty Dog within Sony who spent nothing close to what PD spent on GT5 are getting games out faster and are probably making profit to higher degrees and deliverying, arguably, better graphical fidelity (something PD were known for, making PS hardware bleed), even with lower sales, just because they're better structured.
I think someone from Sony worrying about the cash and management and hiring and Kaz worrying about development, production and the game would actually be better for the game, Sony can be pretty hands off, as the rest of their studios know with the exception of forcing 3D or whatever product Sony wants to push, but they're never actively set down and FORCED a studio to meet an already over extended submission date, a date PD still missed.
No, PD without Sony wouldn't even get a game off the ground, no one would take the risk. Sony only do because PD is guranateed sales.