[fjtorres]

The issue isn't necessarily about specific vendors vanishing. Though, of course, indie bookstores can and will go out of business as they have been folding, piecemeal, for decades now.
The retail issue facing the industry is how much aggregate shelf-space will be available for print books and how it will be allocated. Borders vanishing took out a big chunk at once but that is not the only way shelf-space is declining; B&M retailers can and are devoting more shelf space previously devoted to pbooks to other products. B&N, for example has been moving floor space from books to games and toys. If they reallocate, say, 10% shelf space, that would be the equivalent of 40-some stores. And B&N has already been quietly closing stores on a case by case basis. Add it up and you could be looking at the equivalent of a small chain, 100-stores worth, vanishing over a year or so.

A second issue is what the remaining book shelf-space is allocated to; how much gets allocated to the annointed "bestsellers", how much to the midlist, and how much to the backlist. The superstore business model was originally predicated on stocking a deep catalog (for the time) but the rise of online retailing raised the ante for catalog depth to levels no B&M retailer can profitably match without adopting POD and that doesn't seem to be a high priority for most of them.

The near term challenge is unlikely to be another catastrophic implosion but a steady, sustained erosion of shelf space, and greater competition among publishers for it is more likely. Dont be surprised to see B&N and/or BAM follow Indigo's example and demand marketting fees from publishers just to stock their books as well as returning more books and starting deep-discounting sooner in the release cycle.