No format lasts forever. The file format, the software to play it, and the hardware on which it is stored will eventually be obsolete and unusable. This is a significant problem in libraries and archives. Unlike paper books, most new formats have a very short lifetime.
The best strategy seems to be to put the data into a widely used format. The more standardized the format, the more likely there will be software to play it. The files themselves should be kept in the latest hardware Copy the files to your newest hardware when you get it.
For instance I have files on magnetic tape (from a Commodore PET), 5.25 inch floppy disk (IBM PC), 3.5 inch floppy disk (PC format), Iomega ZIP disks, CDROM and DVD. I can read the last two on my current PC, I have an older PC that can read the 3.5 inch disks, and has a parallel port to connect the ZIP drive. Fortunately, I also have copies of all the files I care about on my current PC hard drive. I keep copying them to newer PCs as they come along, and when needed I convert the file format (like from WordPerfect to Word documents).