I would like to contribute this feature and have a pull request ready for review. Approach:

• The AuditLog plugin subscribes to the existing beforeSurveyDelete model event. Core already fires it from Survey::delete() after the permission check and before any related data is removed. No core file changes.
• This covers every normal way to delete a survey: admin single delete, admin bulk delete, RemoteControl delete_survey, and the cleanup after a failed survey import.
• One row is logged with entity survey, entityid = survey ID, action delete, and uid = the user who deleted it. oldvalues holds the survey attributes plus the survey title in every language, so the survey can still be identified after it is gone. The bounce account password (bounceaccountpass) is left out, the same way the user password is left out when a user is deleted.
• New global plugin setting "Survey deleted", on by default. The "Survey settings" heading in the plugin settings is renamed to "Surveys" so both survey entries sit under it.
• The per-survey "Audit log for this survey" setting is deliberately NOT checked for this event. That setting is about person-related data. If it could suppress this entry, a survey owner could switch auditing off and then delete the survey without a trace, which is the situation this ticket describes.
• Not covered: the data consistency check removes orphaned surveys with deleteByPk(), which fires no model events.
• Possible follow-ups, not in this change: other events that are not logged yet, e.g. survey activation/deactivation and question/group deletion.

Target branch: develop-minor. Unit tests are included (tests/unit/plugins/AuditLogTest.php).
Feedback on the approach is welcome, especially on skipping the per-survey setting.