What are the grounds for permanent deletion of a question on this group? That is: total deletion with no-one able to see or undelete the question.
Moderators redact content that contains contact information (like email address or phone number), personally identifying details, passwords, or connection strings. We will often honor a request to redact content that may have potentially harmful impact to a poster as well -- this doesn't usually happen on EL&U, but occasionally happens on SO or Workplace, for instance when someone has inadvertently posted proprietary code or revealed trade secrets.
We can redact both posts and chat messages. Redactions of posts have to be approved by a second. Any time we redact an edit or purge a chat message, that action is logged and the community moderation team is made aware of it.
Otherwise, editing or deletion is sufficient.