Life, Death
Despite every precaution against it, the third archdruid still eventually died from old age after more than 5 centuries at the post. As such his death had been expected for a while and a replacement had already been chosen.
Considering that the third archdruid was a half-elf, he lived far longer than what was typical for his race. Due to this, a covert power struggle had already been going on for over a century, and when he finally died it had already been won. The fourth archdruid was an elf, who had been a senior member of the organisation for a long time. He was chosen as a replacement due to his unusually fast decision-making skills in elves and his ability to lead those under him. Despite this, he had much to prove to those the order and quickly set out to succeed where his predecessor had left off.