If the password is securely hashed, and the attack only includes data exfiltration, then there’s theoretically no risk of breaking into users’ accounts anyways. However, the issue is that if somebody can log into your Plex account, that means they got your password somehow - and if they did get that password, they can use it elsewhere. So if there’s any reason to change your password on Plex, then there’s just as much reason to change that same password elsewhere.