An outcast elephant who prefers to keep to himself becomes an unlikely hero when he unintentionally prevents a tragedy from occurring, but now he must learn how to become a leader.

I like the idea, but you need a specific villain, maybe a crocodile.

If he were the hereditary leader, in other words, if it's his birthright like in the Lion King, he would have a more compelling reason to rise to the occasion. Otherwise, I have to agree with Richiev and DPG, the logic behind the nature of his leadership ascension doesn't work.

A shy, cowardly elephant makes up a story of heroism and is made leader of his tribe, but when a real threat emerges he must lead his on a perilous journey to new land and safety.

Currently your elephant becomes a hero and then isn't challenged as nothing is forcing him to become a leader and his hero status isn't being threatened the two parts seem unconnected.