I have Nooks, a Sony and Adobe Digital Editions. ADE means I can buy books [or borrow from my library] from a variety of vendors - of the many that sell Adobe epubs - for all my readers. I'm not tied to B&N or Sony's store, nice as they may be. And ADE is, IMO, really straightforward and easy to learn to use. The additional step of sideloading is required, but I personally prefer it to having my device handcuffed to a single vendor.
B&N uses your CC# to generate the DRM for your ebooks, so theoretically, as long as you have the number & the file, you should be able to unlock your books. I've put a few of my B&N books on my Mother's Nook and have been able to unlock them that way.
I had to return my NookSTR for a faulty battery, and the experience was painless. 15 minutes on the phone, 2 failed resets and the rep mailed me an RMA and shipped a replacement unit that afternoon. Big City Mom - in her 70's - took her unit to an actual store, and they were patient and fixed her problem promptly.
But the advice to strip and back-up is good - it is the only way to assure your books remain available in the future. A book I purchased through FeedBooks 2 years ago still shows in my account, but I will have to re-buy it to download another copy. The MS Reader LIT books purchased through Amazon? Don't even show in my purchase history.
* Sony hasn't authorized the B&N DRM, so presently B&N books are Nook-only, I believe.