Drawings created in the 1960s and exposed to light are already showing loss of color. Sepia and diazo prints will degrade slightly each time they are exposed to light during research use. The adhesive used on sticky backs has tended to degrade, causing the labels to fall off the paper, linen, or Mylar, thus separating essential information from the drawing. These should be reformatted immediately. The greatest challenge, however, is preservation of electronic media.
Nothing is permanent.
Currently CDs are probably best but they will be affected by storage conditions and may have substrate degradation over time. Architects and archives must build in a data conversion process to new technology every 5 years or sooner.