When accounts go inactive--looks like you give them 2 years?--an existing user can change their player name to that account. But what happens to the stuff of the person who had that account? What if that player comes back after their hiatus? Is that username also available to new players signing up for the first time?
The username should also be available to new users, but I know that pet names sometimes glitch with creating a new pet (special pets, mostly, like a Bumbus). Your account and all its contents stick around once it's gone inactive, that's the point of them going inactive now instead of being deleted. Users are given a free name change if/when they return.
It's also one year of inactivity before the user- and pet names are available for clearing c: