Engadget is reporting that Microsoft has made an offer to buy Nook Media, which is set up to handle the Nook e-reader, tablet and college bookstore business arm of Barnes & Noble and that if the sale goes thru, the academic arm will be shut down and Nook tablets will dropped sometime next year, leaving them to concentrate on the app running on third-party tablets (such as Windows 8 devices and MS Surface, perhaps?).
Those investing in eInk readers don't appear to need to worry, though, "as the leaked documents state that Nook Media's e-reader division won't be killed off". Of course, even if B&N stops creating new tablets, that doesn't really have any bearing on you using a tablet you've bought recently or even later this year; tablet generations are running at only about a year, so by mid-2014, an entirely new generation of devices will no doubt be released by multiple vendors.
What this might mean for the Nook ebookstore is a little more unclear. I suspect nothing much (especially in the short term) and that it will run as-is (perhaps without offers to get you into the store with BOGOF deals), just with Microsoft at the helm. Even if they eventually kill off the proprietary DRM, their past track record on the LIT format suggests that the licensing servers will run for many years, even after they stop selling any books.