I have a number of sites using pretty old 3rd party themes that to the best of my knowledge are no longer updated / supported. I’d like to persuade some of my clients to part with a little cash to get them onto a modern framework, but what is the likelihood of an old theme ‘breaking’ some functionality, and what would be the main causes? Clearly, Having a dozen broken sites that need rapid fixing would not be great!
The only theme I can personally recall breaking was actually pretty new - Depth (just after Nick Cates departed) - where the scrolling parallax effect completely broke on Safari due to a Javascript library issue - kindly fixed by Joe Workman.
The old themes I still have in place include some from BLT, Michael David and Henk Vrieselaar (I am aware the Will Woodgate supports some of Henk’s old themes) . Still holding up well at the moment but …