In this case the username is probably not PII, but in many cases it is considered PII by GDPR legislation. it would be nice if upon account deletion there would be a way to know that the username exists in post content and possibly an automatic way to clean it up.
Yes, I know, and if you add the original username to the censor and add 'Deleted member <number>' to the Replacement field it will replace the original username throughout the forum where ever it shows.