If Sony is capable of winning this holiday season, then the chances that the PS3 will outsell the 360 will be favorable. The PS3 has done noticeably well the first half of this year. However, the 360 holiday lineup is no pushover and the economy is stark. If the 360 wins, then Sony has to vie for long term.
Unless Sony files for bankruptcy, there is very little doubt that the PS3 will be offered for 10 years. If the PS3 sticks around longer than the 360, then the feat is possible. Whether or not it matters by then is a different story.
The PS3 still has quite a few potentially huge, announced exclusive games that have not been released. Who knows if this is also the case with the 360. Speculated titles for the 360 might just end up appearing on the next generation xbox. At least Sony is currently providing the PS3 enough drive to sell decently into next generation.
If the PS4 continues using cell, Sony can offer the PS3 for cheap while pushing the PS4. All Sony needs to do is upgrade the specs of the PS3 and increase blu-ray drive speed for the PS4.
The 360 is already at a low price and is still selling modestly unlike the PS2. If this trend continues, it is difficult to say if Microsoft would be willing to keep the 360 around once the next wave of consoles hits shelves.