Leave 'em sealed up and store in equable conditions. You never know when some loophole will be found, and there will always be cracking good playing decks in existence somewhere. Even if the original tapes are lost, you know that the material is not lost. Miracles have been worked with records much older than yours. You are a very important person! Beware of sending 'em to some large organisation where their value may not be appreciated. No centralisation. The best form of defence is a gun on every rooftop... ;-)