Dave Coffin's dcraw.c source code (which is able to process raw files from existing cameras) is open source.
Unless Nikon decides to be really stupid from a PR perspective, and tries to prosecute the developers of raw converters that can process .nef files under the DMCA (Digital Milleninum Copyright Act), you really don't have anything to worry about.
I compile newer versions of dcraw.c on a regular basis, and use a variety of products that include libraries based on dcraw.c (which are easy to recompile on any platform that has a C compiler available as newer versions of it become available).
I don't think the vast majority of third party developers are going to suddenly stop supporting older cameras (although camera manufacturers have pulled that stunt in the past).
As for storage media, I do upgrade. I copy older data to newer drives each time I upgrade. That way, I have a lot of disk drives with my data on them (including older floppy disks, MFM drives, IDE Drives, SATA Drives, etc.).