If they just deleted half of the PHP-Nuke install then there is not much you can do other than to remake the pages in Wordpress, or whatever you are now using. I don't personally understand why someone would be using a CMS and just bodge the move to a different CMS in such a way. Must have been some really crap people running that site originally is all I can think.

If you really cannot get into the admin backend of php-nuke then the only other option would be to try and hack the database and find where the html image code is being stored in the tables and edit the entries manually. There is the danger that you could mess up a table or the whole database and render the whole site dead.

To me it seems that the site has been completely buggered up and needs to be started again!