As I replied when you asked this question in another post last week. There
is NO WAY to support this kind of scenario  in SharePoint. developers  can
not make changes  to existing pages in a separate environment  and then push
the changes to SharePoint. SharePoint isn't designed to work that way. One
of the main design goals for SharePoint was to empower users to maintain
content for themselves in production. You cannot maintain live content  in
two separate systems and then merge the results.

In case you don't remember the original reply I've copied it below. That
was and is the answer to your question. Just because its not the answer
that you want to hear doesn't make it wrong. Asking the question again
won't change the response.

SharePoint isn't designed to allow content changes to be made in both a Dev
and Production environment. It does support using a dev  environment to
create artifacts like web parts, event recievers, workflows, etc that are
then deployed to the production site as solutions. All content changes
should be made directly on the production system, not in a Dev environment.
One of the strengths of SharePoint is that it expects users to add and
maintain content to the system not developers. Developers should
concentrate on building better tools and infrastructure to be used by end
users to maintain content.

Is it possible to contain all changes  in a source control environment  and then
merge the differing pieces together? Maybe a continuous integration, of sorts?

Unfortunately it doesn't work that way. The contents of a page  on a page on
a SharePoint site all come out of the content  database for that site. They
are more likely to be entries in a list or library displayed by a web part
than to be actual physical changes  to the page. Even what webparts show on
a particular page and how they are configured is actually stored in the
content database and are not direct entries on the page in most cases. That
kind of dynamically assembled content is one of the advantages of
SharePoint. A Dev/Test/Production environment  for content just doesn't work
given how SharePoint is designed.

My understanding is that this would only work if the changes  that the
devs were making  were *not* at the content  level. Say if they were
making changes to custom workflows, webparts, eventhandlers and that
sort of thing. These changes could be deployed from dev  to authoring
and then into prod...

It can't be done.

You can't take an item move  it from a live environment  to a test environment.
Make unknown changes  to both the live and test environment and expect a good
outcome.

You have a SQL database, back  it up and restore it to a test environment, and
develop on it.
Meanwhile the authors  are add tables and rows to the live database.

How does the developer restore the database without overwriting the changes the
authors made? How do you verify that the data is good? How do you know what
the developer has done won't modify the changes the authors have made?

Forget it being an author and dev  site. PLAIN AND SIMPLE IT'S 2 DEV SITES. YOU
CAN NOT HAVE TWO DEVS MAKING DIFFERENT CHANGES TO THE SAME APPLICATION WITHOUT
THE DEVS/AUTHORS WORKING TOGETHER