The whole question of which media to use for long-term archival storage of audio is a HUGE problem. There are ptoential problems with every media type that can cause the content to be lost -- cassettes lose their pressure pads, DATs have drop-outs, hard drives are mechanical devices that will eventually fail. We don't really know the shelf-life of CDs (the "archival" ones claim that they'll last 100 years, but that remains to be seen).

Short of cutting new phonodisks, reel-to-reel is probably the most stable format. But the supply of both tape and players/recorders is not going to last forever.

'Tis a quandry...