While an advisor is the second in command, they are NOT the one who takes over leadership when the commander dies. Instead, when a commander dies, any cat may attempt what is called the Seasonal Trials; Long ago, the gods had gifted the colonies five artifacts. A cat with all five could speak face-to-face with the gods, and receive blessings of power and wisdom, as well as the right to rule over their colony.
These artifacts were hidden across the territories, each cat participating at the mercy of fate and destiny to find each one. When the Goat was exiled their artifact was banished as well, reducing the number to just four artifacts. There are no rules to the Seasonal Trials, only to find all four and gain control of the colony.