Assuming that consoles tanked for some reason (and disregarding the Valve Box), I doubt it'd help PC gaming much at all. Big AAA type games nowadays have tons of money dumped into them, requiring a huge install base. The only way you're going to get a massive install base on current computers that's roughly equivalent to the combination of Wii, Xbox 360, and PS3 is to start churning out games that'll run okay on integrated graphics chips one or two generations old. Imagine what your average console gamer will say when they try to play CoD6 on an Intel HD4000 in their laptop and wonder why the hell it looks so crappy compared to their Xbox 360. Though maybe it'll wind up something in the middle: budgets will get a bit more sensible, PC-specific engines will run better than quick port jobs, and OEMs will put out reasonably priced and specc'd gaming PCs. Because, let's face it, most people that would be migrating to PC gaming don't know what a video card is, let alone would be willing to part and build their own PC.
And then there's the issues Zenoth mentions and headcase hints at: reuse of existing pre-ported engines, chunking in whatever assets they can on a reduced budget, and releasing Yet Another Call of Black Ops 17, cause that's all they can mange on their reduced budgets and install base.
Now if some companies manage to absorb the cost and put out some top-notch games that pushed the hardware envelope and nudged people to buy higher end computers or components, then there might be more of a shift. Which would probably continue until small form factor PCs with components in a suitable budgeterformance envelope became common place installed in the living room. And then you'd have 'consoles' again, though probably based around PC architecture. Then again, we're sorta-kinda getting that with the next gen, even moreso if the Valve Box is all it's cracked up to be.
I really do imagine that if the next generation of consoles bombed, publishers would continue making games for current generation consoles and focus more of their development teams to mobile/phone gaming with a freemium model. The mobile install base is huge and people plunk down big money on freemium game models on mobile platforms. Console gaming would become the reliable funder as companies save money by reusing existing engines, assets, and IPs and in turn using this to fund each successive mobile cash cow.