I think if you open RHHTML, then open your RHWord project,
you get a wizard with a whole bunch of import/conversion options. I
haven't done a conversion myself, but you could try it on a copy of
your current project (although I'd be extra careful if you have the
project in source control - I'm not familiar with how that works in
RHWord).
It's probably worth reading the help topics about Importing
Winhelp Projects and Creating new projects with word documents.
(both sub-books under Projects in the RH HTML TOC)