Unfortunately, currently our workflow user interface does not allow sending comments when the page is declined. We plan such functionality in the future but most probably it will be when we release a version for ASP.NET 3.0 and migrate our workflow to Windows Workflow Foundation.
The rollback action actually changes the content of the page, therefore it should be published again. Currently, we cannot provide you a good solution for doing this through code because no event is fired on this action. We will consider it for the next release of Sitefinity.
the Telerik team