Real story on why Lionel never re-released 50's-style Flyer die-cast locomotives?

I had heard that the Flyer steamer dies for die-cast locos were lost or somehow so damaged they were impractical to use once Lionel acquired the Flyer line in the late 60's.    I don't know if this is true or if Lionel simply saw no real need to perpetuate the manufacture of die-cast S gauge locos that it had successfully run off the market after years of competition.   Anyone know "the rest of the story?"