Nah, no chance in hell of it happening. If this was like a month prior to the launch, then maybe. There's a lot of money invested on so many sides for the exact launch date, from advertising to retailers etc. Its a very short period of time for this to have a major effect and too short to do a worldwide early launch. Every game that is released is played before launch by some people, from retailers to pirates. I'm sure Rockstar expected it. The fact that it's less than a week till launch before it happens is pretty impressive. San Andreas leaked sooner I believe, but cant remember really.
Many stores in the US have not received their shipments yet either if at all. One of my best friends is a manager at my local GS and they're not expecting the shipments until Friday or Monday (east coast USA). His boss is a dick though, so even hes not getting it before launch.
Plus, the "leaked" version is only the 360 as the PS3 cannot be modified. Yes, theres definitely some early PS3 people with it but its hardly rampant and most if not all of them are probably retail employees. The 360 can be modified to play pirated games, but the PS3 cannot as of yet. The amount of people with modified 360's in terms of ratio is very very low for a leak to have a damaging impact. They were never going to buy it to begin with anyway.