The only solution I can think of is to write a script to look through the page to find all the fields that have the words “Required Field” in the title and see if there is any value assigned to it.
I don’t think I have any inclination to do this. Perhaps an addition to jQuery one day?
Anyone keen enough could start with something like this:
The answer to How do I trigger the default form validation without submitting the form was that it could not be done.
Whilst not an ideal solution, future readers could look up Save conflict – reset ratings and ratingscount in presaveaction
… the use of window.onbeforeunload may give inspiration.