I wish there was an option for 'none', because I don't think any of the Big 3 will exit after the next hardware cycle.
I picked Microsoft, only because they seem to me to be the least-reliant on game and hardware sales compared to Sony and Nintendo. They make most of their money and focus most of their business on Windows software, and they really don't need videogames to survive. They've done well, and they can continue to do well, but if worst comes to worst and the demand and the console market collapses, they could easily leave and never look back. With their new-found extreme focus on entertainment and video applications versus AAA video games, they seem to be positioning themselves for that eventuality anyway.
Nintendo is the least likely to ever leave, even if the Wii U doesn't do very well. Worst-case scenario, even with GameCube-level sales, which let's be honest, is very unlikely, Nintendo would still stick it out for better or worse. GameCube was still making a tidy profit for Nintendo well into 2005, even after hardware and software sales had mostly dried up.
Sony is also not likely at all to ever leave the hardware business, because as Jack Tretton said, they are unabashedly going after the hardcore gamer crowd, and that's all they care about. That group of 10-20 million people like us who buy early hardware, lots of accessories, lots of games, and lots of downloads. There's a lot of money in that 18-34 demographic of males with lots of disposable income who enjoy spending a lot of money on videogames. That is Sony's bread and butter. It would be stupid of them to give that up, and they well know that.