In theory is probably is possible but you would probably want a developer with some technical expertise to attempt the process.

What I would do is:

• Look at the Moodle version for the Totara site you wish to migrate (the $release variable in version.php)
• Create a test site to try it out (with a copy of your live db and dataroot)
• Replace the Totara code directory with a copy of the Moodle code based on the version from step 1
• Visit the site and see how it looks.

You would then have to fix any problems that came up - it's a bit hard to know what they would be and how serious/difficult they would be to resolve so you'd just have to try it and do some thorough testing. You would most likely have to repeat the process a few times after fixing issues so make sure you have a backup of everything.

Obviously doing this would remove access to all the totara functionality, you may want to go along and clean up the unused tables (drop any table mentioned in totara/*/db/install.xml would be a start).

If you did this I think it would then be a bit risky to re-upgrade to Totara again so I would avoid it unless you are really sure.

Simon