The old Bioware site where the accounts with CD key storage was the target of a pretty big hack a few years back and a good chunk of the compromised resources never came back online. Some say it's because Bioware/EA didn't want to expend the money or effort to bring those resources back online for older games. Some say (particularly with regard to things like CD keys) that there was no way to bring the resources back online without giving the hackers access to thousands of gamer's data, including their CD keys.
Either way, people who had kept a local record of their CD keys were okay in that regard. That includes people who still had an old installation of the game somewhere (even if it's on a machine they don't use anymore or if NWN doesn't run properly on that machine) since the nwncdkey.ini file from that old install would still have the CD keys for them. I mention that because, if you had NWN on an older machine and you need the keys to complete the install on a newer one so that you can play again, you may still be able get your keys off the older install.
For those who don't still have their old keys anywhere, the GOG solution Squatting Monk mentions is pretty viable. $10 is a pretty good deal for NWN, even as a re-purchase. Pretty much all of the custom content (community-made modules, GUI enhancements, art assets, and other things) that give the game thousands of hours of replayability are still available on the new Neverwinter Vault at http://neverwintervault.org/. And, it seems like every so often GOG has a sale with NWN at an even lower price or as part of a package deal with other D&D-related games with a group discount.
