It's kind of a crappy situation, but it's one that we've put ourselves in. I'm not confident that we'd see a renaissance of indie booksellers should BN close.
Personally I think that with Nook, BN for various reasons bungled what could easily have been a very successful product. They might still have been able to turn it around by pressuring publishers to sell ebooks for cheaper, removing DRM, and focusing on a true ereading experience and owning a niche instead of competing with full-blown tablets.
Since they've thrown in the towel with Nook, their only hope seems to be dropping prices to give people a reason to walk in instead of going to Amazon, or to make money on ancillary physical experiences, like drinking coffee while browsing. But they already made a possibly fatal mistake in that strategy by renting out space to Starbucks instead of doing their own coffee thing.
BN closing would be a pretty big blow to books in general, regardless of Amazon's sales. While I can't pity the corporation for being affected by market forces, nor can I pity it considering what it's done to indie sellers, neither do I want to see books completely disappearing from the average American's sight.