How do they decide when to remove an element from production, and what happens to the molds when they are retired?

Question

We all know certain LEGO elements are no longer being produced. How do they decide when to remove an element from production, and what happens to the molds when they are retired?

Answer 1

I can't find a link to substantiate this, but a quality assurance representative from LEGO mentioned at a BrickWorld presentation a few years ago that worn out molds are buried on the factory property in Denmark in concrete. If anyone else can find substantiation for that, I'd love to see it.