Why do you 'need a single regex to do' this? What context will the html superscript tag have when you remove all of the rest of the html tags in a document? Have you looked at any of the modules on cpan designed to make working with html? There are modules with tried and tested code to properly deal with tagged documents, I would suggest you spend some time investigating this route. This sort of question is asked every so often, super search should return some useful results.

Martin