Hello, I am interested in changing ove a deeply indexed HTML page based site to either Joomla or Wordpress. In any case, will the site lose traffic permanatly? Thanks for your advice.
Switching to wordpress (don't do Joomla unless you like a learning curve) will change your link structure and you will need to tell Google where you moved your content. A 301 redirect will do the trick, but it is going to be a bit of fenagaling. Read this thuroughly first: http://en.wikipedia.org/wiki/URL_redirection