First – there is hope! I have been going through the same process. I am not so good at reverse engineering – but I am pretty good with cut & paste.
Look for a matched set of a WP Theme and a website Template. Compare them and see what modifications need to be made. Then make the same modifications in your WP to fit your site. At least that is what I did…made the Theme CSS mimic the site CSS – cam colors, graphics, etc
I don’t have it up just yet, but a general user will never see the difference at my site.