I know this is possible, I achieved a very good result back in April after a fairly brief search of the internet for a method. It was so easy I didn't feel the need to record the method, or where I found the advice. Yes, I KNOW how stupid that was.
I am at work, so no possibility of updating software or using Mif2go. Not sure that Mif2go would work on such primitive files anyway. I am using FM+SGML 5.5 to create unstructured files arranged in a book file. I need to convert these files, individually or as a book, to rtf, preserving as much as possible of the formatting.
I seem to recall Acrobat Distiller being involved in the process I used before. I still have the resulting file, which has retained all the paratags. I think I had to tweak the para definitions and replace the headers and footers. Cross references are missing. I have had no luck recreating the method, or finding it again on the internet.