JQuery :: Replacing Form With Submitted Content

What I want to do is replace a form with the submitted content. As an example, The form is submitted using the jquery.form plugin. The content is saved to the DB and a rendered comment is passed back to the client, and the success callback then replaces the form with the content. Simple enough. However, if server-side validation fails, I want to render the form, along with validation error messages, and insert that back into the client page, i.e. replace the first form with the second (which also contains the submitted content). Also straightforward, except that, on a truly successful submission, I'll need to do some other things on the page. If validation fails I only need to display the form with errors. I can think of two approaches. One is to search the returned data for some string (e.g., "<form") to decide if the other tasks are to be run.

The other is to send back the data encapsulated in a JSON object, eg:
{
'status': 'FAIL',
'data': '<form ...'
messages: '...'
}