Soniccouture is offering a selection of free Kontakt libraries in the Free Stuff section of their website. After signing up for a free Soniccouture account, new users will receive the serial numbers required for library activation in Native Access.
The truth is that any challenge-response based copy protection system can and will go offline. Unless it's just a serial number or something stored 100% in a dongle, when the company stops issuing responses, your product will no longer be re-installable.
They could have designed Native Access to better support their original copy protection. Maybe. I doubt we'll even know for sure what tipped them this direction. Some sort of unlock generator might be possible (if pirates can do it, they could do it too). Or they could fix Kontakt to not block products protected by the old license scheme. For the plugins those are all NI products, in theory they could just rebuild them to not do challenge-response and just take a serial number. 1e1e36bf2d