I agree that the economy will always need the large retailers to sustain itself. However, I think there will always be somebody to fill that void. I've got a webpage where I sell stuff, so do thousands of other people. If WWBW and guitar center goes under, why couldn't I become one of the big players? Or you? Or somebody else. Less customers going to them, means more to us, and inevitably the person with the best SEO optimization, the best prices and the best customer service will rise to be the next "big seller" which will keep the sales volume up. There are a few contenders out there already emerging (I'm not one of them...yet).
As for buying direct from manufactures, yeah, some do it. But I don't see it catching on. Companies use dealers so they don't have deal with customers on a regular basis. It's the same reason 80% of my instrument repairs are done for music stores. I don't mind making 20% less on a repair if they take care of finding the customers, billing the customer, actually collecting the money etc. etc. I drop off the finished product, get paid right away and move on. Worth it (for me). I think many major manufacturers have a similar outlook.