Personally I wouldn't bother fixing it just have a warning that says "This version of Internet Explorer is no longer supported. Please upgrade to a ......" (I took from gmail) So they know if they continue this isn't how the webpage is suppose to look and may behave badly because of it. Or something along the lines of that
I think IE 9 is about as far back as I'm willing to go. So I would like to get that working, but you are right, anything older and I should have a warning.