You should, as a rule, have three digital copies of your project. In addition to the original interview, create a master copy that can be used for duplication, as well as several duplicate recordings. Store a few and share the rest.
Remember that digital technology is always evolving. You may have the most up-to-date equipment today, but there will probably be a game-changer invented tomorrow -- or in the next few years, certainly. As newer generations come to light, you may need to convert your interview to those formats.
Refreshing the interview using new technology extends its life. However, it's also a good idea to have a paper transcript, but only if it is acid-free paper. Pay attention, too, to the storage environment. As a general rule, too much of anything is bad for your oral heirloom. So keep it out of the sun, away from heat or cold extremes and protected from water and humidity.