Elephant have six sets of molars in their lifetime and as a tooth wears out through relentless grinding another pushes forward to replace it.
Each successive set of teeth will last for a longer period of time until the final set appears at about 30 years. The worn down teeth wear off into a shelf which will eventually break off and fall out.
When this happens the elephants will seek up a place where the vegetation is easier to digest and eat. Elephants in this predicament often die of starvation or malnutrition.
ANd that my friends is why we talk about "AN Elephant Graveyard", and yes they do exist.. And yes a whole herd of elephants do mourn when loosing a member, just like us humans. But then they walk off because they know that energy cannot stop, it will only take a new form. So nothing is ever really gone.