Clarifying delayed durability
I'm afraid you misunderstand how transactions with delayed durability work. There won't be a magic rollback after a reportedly successful commit -- the client application will not know if the changes it thinks have been committed are never actually persisted. As described in the documentation, in the delayed durability mode the server reports a successful commit immediately, but delays writing the log buffer to the disk until some time later. If the server crashes or shuts down before then, these changes will be lost and the client will not know about that.